starter48

You have described another old issue. UT 3.3.1 introduced a new problem: at WinXP icon appears empty, but not missed. You may click on that empty space to activate UT window.

They used same UPX but they stripped UPX header at offset 3E0h, that conatins compression method and checksums, so UPX can't unpack it anymore. You may compare "old" and "new" utorrent.exe at offset 3E0h-400h to see the difference. "New" utorrent.exe can be unpacked still with 3d-party external unpacker that traces stub till program entry point (something like procdump), or header info can be recovered manually from stub's code to unpack it with UPX natively.