Problems with porting PocketQuake. Please help me !!!

I write Quake I port for Nokia Series 60 devices.
I would like to use PocketQuake as base for porting, but have received the following problem:
At gamma = 0.5 I receive a pictures similar below given. What I do wrong?

I would like to use PocketQuake as base for porting, but have received the following problem:
At gamma = 0.5 I receive a pictures similar below given. What I do wrong?
