Created attachment 8703583 [details] Screen Shot 2016-01-04 at 14.34.23.png Signing in should be quick, even if the first sync run takes a while. Instead, the screen from the attached screenshot stays visible for a very long time.
The 'Signing in...' test is shown during the enabling state only. It should not be affected by the first sync. The enabling state can take longer depending on how fast the requests to Syncto to check the account state are. Maybe you found a slow server response situation. I tried to reproduce this issue with no luck, so I'm closing it as works for me. Feel free to reopen if you think this is still a valid issue.