Just checked online and looks like it happened to me too - my flights for Dec 2010 and Jan 2011 have suddenly disappeared, and now I have a negative APD balance.

Am assuming this is some sort of glitch that they can fix - do we all need to ask them to manually recredit??

I just tried to reclaim those flights online via website, and it states "Your claims have been processed and your account balance updated", yet they still no longer appear and am still missing the APD and SP.