Spherical Aberration is not constant when CTF refinement?

Hi, all,

I used Heterogeneous Refinement for 3D classification and then did Homogeneous refinement (New) with CTF refinement for each class. I found that Spherical Aberration value for one class was changed/fitted to about 2.78 while others still kept in the value of 2.70. This change generates an error like “Spherical Aberration is not constant.” to fail the program when I merged this class and other selected class for new Homogeneous refinement (New). Do you anyone know why and how to resolve this issue? Thanks a lot!