mine was the same after maybe 6 months but i don't use hot.it seems that the plastic it's wearing very quickly .i think it's different than the other type of brushes as none of them wore like this and all my brushes are gardiners.also noticed on the extreme the same problem.i cut a few cm from mines and now use them mostly for balconies as it's gets easier between the rails.
i'll probably order SL brushes from now on as the plastic doesn't wear as quickly