I have a weird issue that started this week. I opened a case with Salesforce and they are not helping me and pointing me to Dev Boards. (I also posted there but haven't received solution and I've had better luck on Stackexchange).
We do NOT have "My Domain" deployed (or want to) but users are being periodically redirected to relogin/use salesforce with the domain we registered a long time ago vs normal NA2.salesforce urls. We haven't tested or deployed the domain (or have any sites published with it). I can't delete the domain - option is grayed out.
It seems to happen when users close salesforce windows in a browser, and try to login again, or click thru to salesforce from an link sent thru email.
Again - seems to have started on Friday (release of Spring 14).
Issue seems to be similar to what TechTrekker reported in this question My Domain Gotchas?
"Before Summer'13 there was a problem where the older pre-MyDomain links wouldn't redirect 'properly' to the My Domain links, eg if you clicked on a link you received from Chatter via email, it would ask you to login again even though you were already logged in, because somehow it couldn't relate the two domains as being the same, probably something to do with how the session cookie was set in your browser."