Step 1: Set the gamerule to keepInventory true and gamemode 1

Step 2: Fly Around in your Tardis with the flight panel

Step 3: Land

Step 4: Spawn Bessie in the Tardis

Step 5: Get in Bessie

Step 6: Click on the Tardis Doors

Step 7: Look around for your Tardis. Then try moving around. You may notice that you can't move and that you're in some random location.

Step 8: If you manage to move summon the Tardis with the key

Step 9: try entering the Tardis, you'll keep getting put back some steps very time you try.

Step 10: Do /kill

Step 11: Summon your Tardis again with the key

Step 12: Try entering it

Step 13: You may encounter isssues

Step 14: You will remember Bessie didn't leave the Tardis with you. You will also notice that Bessie did not stay behind in the Tardis.

Swd, please take a look into this issue

That's some serious issues @_@ Hope you can sort it out!