Yahoo! Messenger had a very annoying problem, text selection with Ctrl-A was done when it shouldn't be done.
For example Windows maps AltGr key to Ctrl-Alt keys combination, which is default behaviour. Yahoo! Messenger treats AltGr-A as Ctrl-Alt-A but then it gets the Ctrl-A part, whole text selection, and afterwards it goes to normal keyboard handling, which with a certain Romanian keyboard layout generates the character "ă", but because the text was selected before, "ă" was the only character left in the sentence you wrote.
This was very annoying, but then by using the wonderful Microsoft technology called Detours I was able to intercept certain WIN32 API Messages and prevent the text selection from happening. Yahoo! keyboard patch was created.
Cristian Secară was very nice to host this patch on his webserver, also he made some very good suggestions which improved whole the quality of the software.
The patch is available at this location (Romanian language only).
Note: this patch also works with other keyboard layouts, for example the Hungarian default keyboard layout can be used to generate the character "ä" now.