I have this same problem, but it has been since 1.3.2. I log onto a server and just start falling as if ive fallen bellow bedrock. An answer for iRiiNG's question and mine would be greatly appreciated.
i Fixed it Yesss
First
1) Go to C
2) Windows
3) System32
4) drivers
5)etc
6)copy hosts and place it anywhere
7) open hosts with notepad
8) Delete any Minecraft word in hosts
9) Save it
10) replace it with hosts in etc
11) Have fun !
BTW : i didn't have this problem in 1.3.2
First
1) Go to C
2) Windows
3) System32
4) drivers
5)etc
6)copy hosts and place it anywhere
7) open hosts with notepad
8) Delete any Minecraft word in hosts
9) Save it
10) replace it with hosts in etc
11) Have fun !
EDIT: whilst in hosts, do i delete anything to do with minecraft or just the word minecraft? :3 thanks