I've been fighting with a login issue for the past few hours thinking it was my fault. I'm tired, so my IQ is cut in half right now. Makes for a very plausible scenario. However, I finally tried it in Firefox without issue.
It's just a simple login form, where the action is supposed to log me into both the secure and insecure domains. Here's the action:
action="{module_secureurl}/ZoneProcess.aspx?ZoneID=51&Referrer={module_siteurl,true,true}&OID={module_oid}&OTYPE={module_otype}"
That looks right to me. I also checked on my own site's login and had the same issue. I had just never noticed before because I don't use my secure domain.
Looks like either a bug in BC, or a bug in Chrome. Either way, I think it's worth having BC look into.