4.5 opening multiple circuits for a single page
I don't know whether it's related to the new code to "hold" a page to a circuit, or that being announced made me glance that way for an explanation, but the 4.5 release is "pick a euphemism for the opposite of successful" in building a new page, on certain sites, with a single circuit - sites that the 4.0.8 release handles just fine.
Two examples are nitroflare.com and uploadable.ch. They're both scripted ad and captcha infested steaming piles o' joy - that try to do the "IP address is a person" voodoo. So, when TBB 4.5 opens at least three circuits, commonly using three exit nodes, just to render the landing page - even if the scripts and captchas are successfully navigated through, the odds of the final click coming from what the server "thinks" is the valid address is less than 50/50. TBB 4.0.8 allows you to inflict that suffering on yourself with a single circuit - which, of course, uses a single exit node. And, it does so consistently. TBB 4.5, from what I've been able to test, is also consistent - but that's not a good thing.