Problem with an apostrophe.

Here's the problem... I'm writing a post and I inadvertently hit some key or other - I don't know which one - and from then onwards whenever I try to use an apostrophe (') the cursor leaps out of the compose window to a place below it in a 'search' field - asking me to put in some word to search for.....

And I can't find how to avoid, undo or disable this...