Roberto,

not sure if I'm right here but when flag "Compress all files" is on I think also base file list is compressed while they are already compressed by UPX.
I'm talking about all exe and dll: thinBasic.exe, thinBasicc.exe, thinCore.dll, thinVL.dll, ....
All those files are already natively compressed so compressing them save just few bytes while slow down a bit startup operations when bundled exe is executed.

So, in general, only user files should be compressed.
Just an idea

Ciao
Eros