Image plane in Maya (7) seems bugging a lot of people indeed. On the other hand , i don't understand why not displaying your mds on poly planes, with corresponding height/width.
This is the technique since .... wooosh, since the very beginning of modeling tools.
By the way, if you want to find a solution, I think there are some ... SEARCH in a forum is very usefull
Click and browse dude.
Roach told about some .env editing (particularily if using jpg or tiff ...)
Others told about display drivers ...
Others about other solutions.
Well, good luck. Personaly, i won't use image plane setup while this type of topic raises every week almost. :p