Icosohedral virus map with mirror symmetry?

We've been refining an icosohedral virus, and everything seems like it has been running normally, but the final map seems to have mirror symmetry along all symmetry axes... What could be causing this? The parameters we've been using are:

Control parameter file to run Frealign
======================================

This file must me kept in the project working directory from which the refinement scripts are launched.

Note: Please make sure that project and scratch directories (if specified) are accessible by all sub-processes that are run on cluster nodes.

# Computer-specific setting
cluster_type         PBS	! Set to "sge", "lsf", "slurm", "pbs" or "condor" when running on an SGE, LSF, SLURM, PBS or CONDOR cluster, otherwise set to "none"
.
nprocessor_ref       40		! Number of CPUs to use during refinement.
nprocessor_rec       40		! Number of CPUs to use during reconstruction.
mem_per_cpu	  1000		! Memory available per CPU (in MB).

# Refinement-specific parameters
MODE                  1		! 1, 2, 3 or 4. Refinement mode, normally 1. Set to 2 for additional search.
start_process         24 		! First cycle to execute. Output files from previous cycle (n-1) required.
end_process           25 	! Last cycle to execute.
res_high_refinement   7.3 	! High-resolution limit for particle alignment.
res_high_class        10.0	! High-resolution limit to calculate class membership (OCC).
thresh_reconst        16	        ! Particles with scores below this value will not be included in the reconstruction.
nclasses              1		! Number of classes to use.

# Search-specific parameters
res_search           10.0	! High-resolution limit for orientational search.
thresh_refine        50.0	! Mode 4: Score threshold above which search will not be performed.
DANG                200.0	! Mode 3 and 4: Angular step for orientational search.
ITMAX               200		! Mode 2 and 4: Number of repetitions of grid search with random starting angles.
Bsearch            2000.0	! B-factor filtering (when > 0) applied during search.

# Dataset-specific parameters
data_input           run1		! Root name for parameter and map files.
raw_images           ../stacks/start
image_contrast        N		! N or P. Set to N if particles are dark on bright background, otherwise set to P.
outer_radius        600.0	! Outer radius of spehrical particle mask in Angstrom.
inner_radius         415.0	! Inner radius of spehrical particle mask in Angstrom.
mol_mass           31500.0	! Molecular mass in kDa of particle or helical segment.
Symmetry             I  	! Symmetry of particle.
pix_size              3.24   	! Pixel size of particle in Angstrom.
dstep                 3.24	! Pixel size of detector in micrometer.
Aberration            2.7	! Sherical aberration coefficient in millimeter.
Voltage             300.0	! Beam accelleration voltage in kilovolt.
Amp_contrast          0.07	! Amplitude contrast.

# Expert parameters (for expert users)
XSTD                  0.0	! Tighter masking of 3D map (XSTD > 0) or particles (XSTD  0).
PBC                  5.0	! Discriminate particles with different scores during reconstruction. Small values (5 - 10) discriminate more than large values (50 
- 100).
parameter_mask   "1 1 1 1 1"	! Five flags of 0 or 1 (e.g. 1 1 1 1 1). Determines which parameters are refined.
refineangleinc        4		! When larger than 1: Alternate between refinement of OCC and OCC + angles.
refineshiftinc        4		! When larger than 1: Alternate between refinement of OCC and OCC + angles + shifts.
res_reconstruction    6.5		! High-resolution limit of reconstruction. Normally set to Nyquist limit.
res_low_refinement    1500.0	! Low-resolution limit for particle alignment. Set to particle dimention or larger.
FMAG                  F		! T or F. Set to T to refine particle magnification. Not recommended in most cases.
FDEF                  F		! T or F. Set to T to refine defocus per micrograph. Not recommended in most cases.
FASTIG                F		! T or F. Set to T to refine astigmatism. Not recommended in most cases.
FPART                 F		! T or F. Set to T to refine defocus for each particle. Not recommended in most cases.
FFILT                 T		! T or F. Set to T to apply optimal filter to reconstruction. Recommended in most cases.
FMATCH                F		! T or F. Set to T to output matching projections. Only needed for diagnostics.
FBEAUT                T		! T or F. Set to T to apply symmetry also in real space. Not needed in most cases.
FBOOST                F		! T or F. Set to T to allow potential overfitting during refinement. Not recommended in most cases.
RBfactor              0.0 	! B-factor sharpening (when  0) applied during refinement. Not recommended in most cases.
mp_cpus               1		! Number of CPUs to use for each reconstruction job.
restart_after_crash   F		! T or F. Set to T to restart job if it crashes.
delete_scratch        T		! Delete intermediate files in scratch directory.
qsub_string_ref  ""		! String to add to cluster jobs submitted for refinement (only for SGE and PBS clusters).
qsub_string_rec  ""		! String to add to cluster jobs submitted for reconstruction (only for SGE and PBS clusters).
first_particle        
last_particle         
frealign_bin_dir      
scratch_dir           

# Janelia-specific parameters
night_queue           F		! T or F. Set to T to use night queue.
reschedule_if_qw      F		! T or F. Set to T to reschedule jobs on the normal queue if some end up waiting on night queue.