I was going to do my daily steel-aluminium trade, and I was asked to prove I was not a robot. On the capatcha, I hit the 'prove you'r not a robot' tickbox, but submit before the test box came up.
I received a message telling me that I did not pass, but I hit the trade button and it took me back to my trade screen where I could continue trading unimpeded. No screenshots/link because I haven't had a chance to replicate, and I didn't know the bug(?) existed at the time.