Disable Holster Function? Phone thinks its in a holster when its not

My 8900 has been acting up for a week. i noticed the holster wasn't working anymore, so i replaced the holster. Was not the problem. Last Friday the screen was turning off randomly and none of the buttons did anything. I would be texting and the screen would turn off, then when it turned back on, my text was saved as if i put my phone in the holster during a text. When my screen is black, i still receive calls and texts, but cannot view anything on the screen. It thinks its in the holster.
If i can only disable the hoster function, i wouldnt have a problem. I took the battery out, swapped it with my wifes 8900 battery, didnt help. the screen comes on every once and a while, but only for a short time. any suggestions?

A colleague of mine had this happening to his 9700 a week after getting his new phone and had to have his phone changed.

Just a guess: The holster works via a magnet. When the magnet is close, it must pull some "switch" inside the phone, or it senses the magnet in some other way. Are you subjecting your phone to any magnetic forces?
Otherwise I guess it's going to need a trip to the shop.