Found some more:
Follow these steps:
1 Enable compiz, add itask-ng and set itask-ng transparency to zero (fully transparent)
2 Disable compiz: you'll get the black section on your screen due to itask-ng trying to use composite for it's transparency
3 Remove the itask-ng: everythng turns back to normal
4 Re-add itask-ng: the black section appears again.
When i first used the itask-ng it had no transparency option because i didn't have the composite module disabled, the ability to set it transparent only appeared after compiz was enabled so somehow itask-ng fails to detect compiz isn't enabled anymore.
Gonna look further into it, possibly it will be solved by disabling composite, removing itask-ng, (maybe disable/re-enable it in modules), clean up itask-ng config (if i can find it) and itask-ng this time without composite enabled.
I'll be back soon when the kids are in bed then i'll have time to try out some options and file a bug if i can track down what's going wrong.