I also ran checkbox for Clean SteamCMD and did update/validate to get rid of the 276.13 Holiday update, and move onto the current as of now 276.3 and my server is still running 276.13.
GAME SERVER ID #53117 TICKET#612197
Edit:
After making a change on the control panel that I didn't know would create a new map, I had to load my most recent backup save (only a couple hours old) to recover. When I loaded my backup save with clean steamcmd folder and update/validate selected, I was no longer stuck on the 276.13 holiday patch and updated to 276.3. So, if people are still having issues with this, it might be worth a shot to try to load their most recent backup save (my save was NOT before I added the holiday patch) with the clean and update/validate options selected before hitting save and restart game server.