Sorry to re-create this bug, but after some searching, I think there's no open issue currently tracking this precise problem.

Original issue (marked Resolved): MC-34947

Quoting one of the commenters on MC-34947: this describes our situation:

"I can consistently produce this error by successfully logging into the server, clicking disconnect, and attempting to reconnect to the same server. The screen pauses at "Logging in..." and then gives this error when the login times out."

We're still seeing this in the 1.7 pre-release (another user has commented the same on the original issue)

The problem repro's consistently on both Windows and Linux hosting; across multiple players on my servers, for the last few snapshots.

Not sure how big the impact will be if you roll out 1.7 update without a fix, but worth thinking about!