Alt Login Problem - Bug or Feature?

I have a few alts that I use mainly for testing animations I create and then taking pictures for eventual promotional purposes. I haven't had any problems logging in myself and one or two alts simultaneously until last night.

Last night, I could not login in the alts while I was on with my main account. The errors took various forums. Sometimes I got an error message something like "login failed - login server did not receive login request packet" or something like that. At other times, the attempts would hang and crash either on the "Connecting to Region" message or "Waiting for Region Handshake Message" (the latter message I do not recall ever receiving before).

I did some testing to determine if something was wrong with the alt accounts, or the regioins into which they logged. What I discovered was that I could only successfully log in with any account, but only if none of my other accounts were logged in. With whichever order I tried logging in accounts, the first one was successful, and the next would have trouble as described above.

Changing login regions (with "Edit - Preferences" did not affect success logging. Neither did it matter whethere I were attempting login with multiple instances on the same computer, or logging in from different computers.

I'm wondering if this is some sort of bug related to others currently afflicting SL. Or, I'm wondering if this is a new feature about which I had not previously read, to prevent multiple simultaneous logins of accounts with the same e-mail address attached.

Wonder if you've tried it again. I've had this happen, too, and for a while I thought it was a particular RC viewer version, but then it just started working again. My current hypothesis is that somehow the login packets sometimes don't get to the right client, and that this is somehow related to their time of arrival from the SL login server, and that this in turn is related to how broken that server is at the time. But I could also be easily convinced that it's all something whacked on my client machine, and that I unwittingly fixed it by rebooting or something silly.

In any case, it's been working pretty well for me lately. Well, when logins are working at all, that is.

Memory limitation, maybe? Was anything else running on the computer other than SL?