Bottleimp, thanks for providing the test log-in.
My log-in is acting the same as your test log-in.
I use Dreamhost.
Submitted a ticket to them about it yesterday evening.
Unfortunately I have to join this thread. I upgraded to 2.3.3 and now I can not log in to admin.
It acts like it is going to log in, but just returns the log-in page. This is happening on both blogs that I upgraded.