Originally Posted by john_s
There's an interesting thread over at apug where this, or something like it, appears to be occurring in Pyrocat that is mixed in glycol without water. When the glycol versions were announced it was thought that that they would offer much longer shelf life (and it seems that they do) but they can still deteriorate. I don't know if that's because after repeated opening of the bottle some water from the air is gradually introduced, or, as been suggested, there is actually a reaction taking place which is not primarily about water.
Without evidence, none of this can be proved. If the bottle were to collapse due to a pressure change (oxygen consumed), that would be clear evidence that a major oxidation reaction was occurring.