I'm always skeptical of folks asking for methods to bypass a locked tablet's lockscreen, so let me state that this post won't be one of those.

My 4-yo. locked my TF201 today by entering the incorrect pattern several times, and when I tried to unlock the tablet by signing in with my Google account, the screen appears to turns off and it is rebooted. After searching xda-dev and here, I've concluded that this isn't the intended behaviour. Resetting to factory will be a nuisance but not really a big deal, but I would like to know if this problem has been encountered by anyone else and what I can do to avoid it next time.

The tablet is running Virutous Prime ROM with an unlocked bootloader.
The tablet is using a Google account that was created with an external email address (see: How To Create A Google Account Without GMail | The Expand2Web Blog). I can log in to my Google account and external email account using a browser.
I didn't set the tablet to use the Google account when I first booted it; I set up the Google account about a week later.
The tablet doesn't synchronise anything with the Google account - contacts, calendar, etc.
The tablet is connected to my wireless network because it's been receiving emails while it is currently locked.

Does anyone have an idea what might be causing the problem? I suspect it's the Google account not being a "GMail" account, but I can't test that hypothesis.