Hi,

I also had problems with the AltGr key. These could reliably 
be reproduced by holding the AltGr for some seconds (causing 
Windows generating auto repeat events).

Unfortunately the test version at 

  ftp://cygwin.com/pub/cygwinx/XWin.20110801-git-2d9f9305cb559907.exe.bz2

doesn't fix this problem for me.

I discovered that the mechanism in winkeybd.c function
winIsFakeCtrl_L had a problem if PeekMessage cannot obtain 
the next Alt_R message because it is not there.

I prepared a patch that remembers the last Ctrl_L event and 
reacts on a later following Alt_R. It was also necessary to 
alter the order in winWindowProc in winwndproc.c: the invocation 
of winIsFakeCtrl_L had to be done before discarding auto-repeated
key presses.

The attached patch is against the sources of xserver-cygwin-1.10.3-1.

Best regards,
Oliver