It doesn't always affect all players on the server.
When I first experienced this bug, yesterday, the server's owner was also online (nobody else). I couldn't swim, he could. He confirmed he was in survival mode while testing it. I don't know if it was coincidence that he was the owner, or if there was something different about his status or connection that affected things.
Is this related to the bug where hover text is shown for multiplayer chat when you are asleep in bed with the chat option set to 'Hide'? I couldn't find the bug number for that bug.
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Possible Workaround: I have this bug every time I try to join a multiplayer server in 18w07b. However I can join without crashing in the following way:
Start Minecraft and start playing a Singleplayer game.
Disconnect to Return to main menu
Join Multiplayer game
There is a visible gap between adjacent item frames. If the 'hit box' was the same size as the frame appears, which I believe it used to be, you should be able to click whatever is visible behind that gap.
I think this is the same bug as MC-13623
This bug happened to me as described. Does not require powered track - the mine cart I entered was on unpowered track. Also the bug will cause the null pointer exception every time you try to log back into the server.
Client> java.lang.NullPointerException
Client> at ek.n(SourceFile:174)
Client> at ck.a(SourceFile:237)
Client> at ck.a(SourceFile:225)
Client> at ck.h(SourceFile:175)
Client> at ck.d(SourceFile:16)
Client> at cm.run(SourceFile:115)
Client> java.io.FileNotFoundException: http://assets.minecraft.net/1_6_has_been_released.flag
Client> at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
Client> at kq.a(SourceFile:237)
Client> at bhq.run(SourceFile:114)
Client> at java.lang.Thread.run(Unknown Source)
Client> 2013-04-19 10:03:54 [CLIENT] [INFO] Stopping!
For people looking to reproduce this bug. A server using the latest snapshot can be found by looking for Swim Galactica Actual
The same thing happened to me, only when entering a minecart. Using Windows 7 OS.
See also MC-13829
19b isn't out. Also there is no guarantee that 'future version 1.13+' means 19b. It probably will, but it could be next week if we're unlucky.