Tested with GameLogic.mouse.position and mouse over sensor.
It should be working with other mouse sensor as well. If not, please help to test and report a bug.
(couldn't test blenderplayer but it should be working there as well).
(Benoit, this is the same patch that I sent you. I hope it's OOP enough. Looking forward to hear from you on that)
I believe that this was the last "mouse" related bug we had reported. MouseLoook scripts should be working 100% in Blender/BGE 2.50 now \o/