Maintainance mode = Gain weight??

No b/c you are eating the same calories your body is burning. You are probably stuck undereating. Eat more to lose, many MFP'ers swear by it in getting out of your plateau. That and change up your exercise routine.

It's impossible to say for sure, but if you've been eating the same amount for 9 months and maintaining weight, you ARE eating your maintenance calories. It seems like you're pretty close to your weight goal so this seems somewhat likely.

Keep in mind that this is all an imperfect science. MFP can only estimate your maintenance calories. For me my estimate was high, I manually lowered it by about 150 to lose what I wanted to lose. Then you have your activity level. They are general guidelines and not custom tailored to the 4th decimal place. Maybe your activity level is a bit lower than what you've chosen. Maybe when you record your calories you are overestimating by a small amount. Even 5%, which is almost imperceptible.

Point is, MFP operates on a large number of estimates, some of which involve human error. So when you add it all up it could mean that you're actually off by a decent margin.

Are you measuring yourself at all? Have you seen changes in the last 9 months or are you actually completely stagnant in all areas (body fat, waist/hip measurements, etc)? If you are in fact completely stagnant then I would say there is a high likelihood that you are just in maintenance mode - a little earlier than you wanted to be. Try removing a small amount of calories (like, 100) or doing a little more exercise a day and see if you start moving again. If you do then you know your answer.