Ive been getting this same thing too.
Its blacked out like its a thread i started.
If i had flagged it previously i should be able to unflag it (with the red background), which if i had done previously, i cannot do since the button
is now blacked out and not a black background with a blue text "flag".
EDIT: added pic, quite clearly not my thread. I dont have any blocking software or script jamming, and besides most threads that i havnt started are
fine for flagging and un flagging..
picedit on 5-4-2012 by Biigs because: added pic