Some listed Minecraft servers I play on started to glitch after using 1.2 launcher to play minecraft old-beta b1.0, then switching back to 1.6.1.

What I expected to happen was For the server to behave like normal.

What actually happened was that I went onto the server, and found that I couldn't sprint, eat, activate pressure plates (by walking on them), sleep, craft, smelt, drop things (with Q.), or take damage. I could break blocks, but nothing would drop. I tried breaking a wooden door, and only the top part I was looking at broke. Once, I walked downstairs in my house, opened the door, and was jerked back to my starting point. I checked the door, and it was still opened shortly after, the connection was lost. I tried restarting minecraft, logged back on, And I was still at my spawn point. Several times, on spawning, I was in the same location, I fell through a floor. I restarted several times, and nothing changed. I have not tried this on a single-player world yet.

Steps to Reproduce:
1. start the minecraft launcher, and click edit profile.
2. check the boxes that allow alpha, beta, and snapshot versions. change the version to old-beta b1.0.
3. start the game, and make a new world.
4. save and quit to title, then quit the game.
5. switch version back to 1.6.1 (the server I play on isn't on 1.6.2 yet.)
5.go onto the server.
***note that the server is vanilla, non pvp, and is not large, and not regularly maintenanced.