This is probably a useless bug report, but I have failed to isolate the problem. Perhaps you can find something by dissecting the blend file.

Blender 2.55 r33364

Here is my typical workflow:
1. Edit a script in external editor
2. Load it into Blender's text editor and run it (Alt-O Alt-P)
3. The script creates buttons in the UI panel.
4. Press button which invokes a file selector.
5. Load file
6. Evaluate result
7. Go to 1.

After a while strange things start to happen. Then I quit and notice memory leaks. Typical output:

*bpy stats* - tot exec: 1045094, tot run: 62.1335sec, average run: 0.000059sec, tot usage 3.8039%
Saved session recovery to /tmp/quit.blend
Error Totblock: 15
fileselparams len: 608 0x3ea2008
folderlist len: 16 0x3df1838
text draw cache len: 72 0x3ebb378
fileselparams len: 608 0x3ee1248
folderlist len: 16 0x3f68358
fileselparams len: 608 0x666f2b8
folderlist len: 16 0x923e298
text draw cache len: 72 0x474e6f8
fileselparams len: 608 0x6541e68
folderlist len: 16 0x8e59378
text draw cache len: 72 0x639b148
fileselparams len: 608 0x28624b8
folderlist len: 16 0x726fba8
fileselparams len: 608 0x96bafa8
folderlist len: 16 0x3dcc498

Blender quit