[Zope] ZClasses growing BIG in filesize

When I export my pretty simple ZClass to a .zexp file, the file becomes 17 Mb big. In the ZClass I have a bunch of DTML Methods and Python Scripts and a few External Method. Looking at the list of methods in the ZClass, I can sum up the total size to about 30-40 Kb. The ZClass deals with Photo objects which are big in size. I can't find any hidden Photos that might have sneaked into the ZClass my misstake. (yes I have packed it and made a cache sweep with the default settings) What is the likliest reason for this? Could it be a "memory leak" in one of my Python Scripts that cause the internal Zope cache to cough blood? Help appreciated Peter