...i'm a lefty myself...but i dont really think it's a disadvantage...i think it really depends more on how well you work and communicate with your partner...so it can go both ways...
Well I'd always be more careful at first then if you become long term partners you should be able to have an understanding of each other's habits in taking shots... especially the ones down the middle. I know I have been guilty of some minor raquet clashes with left handed partners.
There's always pros and cons in any kinda formation, they are just different. If the 2 person have good team work, the different hands gives much larger chance in forehand attack (usually stronger). If they have bad communication, then the chance to get a racket clash could be x100 as well.
i have a left handed partner and i'm right handed. we are used to playing with each other, so we rarely have racket clashes.