SuperTux version: v0.5.1
System information: Windows 10
When I drag the cursor over the bottom bar on the level editor with the "Mario's supposed to deal with this..." level in Bonus Island III, the game closes.
Bonus Island 2, not 3, right?
I just checked and I can't really reproduce the issue. Are you comfortable with a debugger?
I was able to reproduce on the Windows build for 0.5.1.

I was able to reproduce this as well. And maybe this part of the level code has something to do with it.
Are you able to get me a backtrace? I have tried it using the wine debugger but got nothing useful.
My system info is:

I don't have a debugger, nor do I know how to debug; however, this is what comes up in the console:
[TINYGETTEXT] levels/monde/en.po:15: error: expected 'msgid': #: levels/monde/info
[WARNING] C:\projects\supertux-o8t59\src\supertux\level_parser.cpp:125 [levels/bonus2/level1.stl] The level author "Kevin" did not specify a license for this level "Mario's Supposed to Deal With This...". You might not be allowed to share it.
[FATAL] C:\projects\supertux-o8t59\src\supertux\main.cpp:510 Unexpected exception: bad allocation
This is pretty much all I can do :/
In the editor for 0.5/0.5.1, there are only two modes for the camera; manual and normal. It's trying to load the mode "autoscroll" but there is no specified mode in the editor for that.
Support for the autoscroll mode would probably help, or the level could just be modified to have an init script to scroll.
We deliberately deprecated autoscroll mode because in our opinion it shouldn't be used anymore.
Why remove it though? If you don't like it, maybe make a message when you select it saying that you shouldn't really use it.
And the auto scroll test level was REALLY cool and original!
@Alzter Is this a still occuring issue?
Seems to be fixed now by the look of things.
Most helpful comment
Why remove it though? If you don't like it, maybe make a message when you select it saying that you shouldn't really use it.