[WinXP] Lyx thinks meta key pressed

[anunbeliever]

Lyx seems to think the meta (alt) key is pressed - ctrl+N doesn't start a  
new document but inserts a new numbered formula into an existing one, the S  
key brings up the Alt+S menu prompt in the status bar at the bottom, and  
I'm not sure what the escape key does do but it definitely doesn't close  
dialog boxes - etc. This behaviour is in Lyx only, and wasn't rectified by  
uninstalling and reinstalling (now on the current 1.6.5). I have no  
keyboard map set in Tools->Preferences->Editing->Keyboard/Mouse.

I certainly didn't deliberately change anything since the last time I used  
Lyx, and I'm not sure what I could have changed accidentally. Any ideas? I  
did a Google, turned up  
http://www.mail-archive.com/lyx-users@lists.lyx.org/msg53492.html which  
doesn't help much other than confirm that I'm not completely batty.

Cheers,
Angus.