the most likely reason is that your MATLAB path contains some (or all)
subfolders of your SPM8 folder before SPM8 is started. SPM8 adds some
folders each time it is started, but these added folders should not be saved
in your MATLAB path. If you need to save the MATLAB path after you have
started SPM8, you should clean up the generated pathdef.m and remove all
paths that belong to subfolders of your SPM8 installation.
Hope this helps,