Thank you very much for not only the queue file but the test files as well, this makes it as simple as pie to test.
Sadly this issue does not appear on my English version of Windows 7.
I tested a Chinese version of Windows 7 running on a VM and oddly enough I wasn't able to reproduce the problem on it.
I reviewed every function and procedure of code related to this and came up with a couple possibilities, I made some experimental changes taking everything I found into consideration.
Can you please try this update (its just the flashfxp.exe w/o the setup)
ffxp5.0.0.3658_alpha41501.zip
These changes effect the way the filename and ext are extracted from the full pathname