Microsoft word crashes when deactive by input method

Question

I am developping an input method. Now I have a crash on microsoft word. When the current edit field is deactive, i need to do some job to clean the marked text. I use:

-(void) deactivateServer:(id) sender
{
     ......
     [sender setMarkedText:@"" selectionRange:NSMakeRange(0,0) replacementRange:NSMakeRange(NSNotFound, NSNotFound)];
}

but when I do it in word, it has a crash for this "setMarkedText". It likes word has does some job to clean the mared text itself. Does anyone have some idea? Thank you.