A .blend file is not needed I think because it happens even on a fresh install and default scene (deleted temporal user and application data folders) of the 2.63 testbuild1,

do :
1) in default startup, go "user preferences" select FILE tab and tick the "compress" files on Save/load menus
2) on the current scene choose "save as..." save
3) a pop up appears "failed opening .gz file" and the result is a -compressed?- file with a ampersand "@" at the .blend extension ( eg. untitled.blend@ )

I think that resulting file loads okay, but, I´m worried about data corruption, in much more complex project files...
You can avoid this by simply unticking the mentioned "compress" flag

As far as I can tell this happens in SVN r 45393+ and 2.63 testbuild1 , and pretty sure NOT in 2.62 svn 45000+ with MiikaH builds (dynamic paint dev)
happened on XP, dont know other systems.

System :
winXP 32 bit
2gb RAM
if you need more info just ask...