RenderWorld tweening alpha problem

I've got my game setup to run like this at the moment:

Timer=CreateTimer(60)

While
GameLogic
WaitTimer(Timer)
RenderWorld 0.5
WaitTimer(Timer)
RenderWorld 1
Wend

Basically so the logic will run 30 times a second, but the user will see 60 frames a second. It runs fine for the most part - except entities with their alpha value set to something not 1. When RenderWorld 0.5 runs all the objects that are supposed to be semi-transparent or invisible will be drawn at full opacity. This happens for meshes and sprites.

It runs fine if I put both RenderWorlds at 1, which leads me to believe this might be a bug. Has anyone experienced something like this before?

I've heard of this problem before a good few times. I can't remember though if anyone resolved it...

Yep encountered that problem too. Don't remember there being a solution, I just stop using tweening. Sorry I wasn't more help.