It doesn't it starts small and then when you expand the window the game stays small
Sorry pushed the wrong botton. I wanted to say that I'm using OSX 10.6.8 in case it helps.
Happened to me too. I'd also like to mention that when I tried to resize the window again I Ninecraft crashed. Here's the console:
Client> 2013-05-10 16:00:52 [CLIENT] [INFO] [CHAT] Saved screenshot as 2013-05-10_16.00.51.png
Client> 2013-05-10 16:00:53 [SERVER] [INFO] Saving and pausing game...
Client> 2013-05-10 16:00:53 [SERVER] [INFO] Saving chunks for level 'testing'/Overworld
Client> 2013-05-10 16:00:54 [SERVER] [INFO] Saving chunks for level 'testing'/Nether
Client> 2013-05-10 16:00:54 [SERVER] [INFO] Saving chunks for level 'testing'/The End
Client> 2013-05-10 16:00:55 [SERVER] [INFO] Stopping server
Client> 2013-05-10 16:00:55 [SERVER] [INFO] Saving players
Client> java.io.IOException: Bad file descriptor
Client> at java.io.RandomAccessFile.seek(Native Method)
Client> at acv.a(SourceFile:306)
Client> at acv.a(SourceFile:249)
Client> at acw.close(SourceFile:230)
Client> at java.util.zip.DeflaterOutputStream.close(DeflaterOutputStream.java:143)
Client> at java.io.FilterOutputStream.close(FilterOutputStream.java:143)
Client> at acy.a(SourceFile:140)
Client> at acy.c(SourceFile:128)
Client> at alk.b(SourceFile:30)
Client> at alk.run(SourceFile:23)
Client> at java.lang.Thread.run(Thread.java:680)
Client> 2013-05-10 16:00:55 [SERVER] [INFO] Saving worlds
Client> 2013-05-10 16:00:55 [SERVER] [INFO] Saving chunks for level 'testing'/Overworld
Client> 2013-05-10 16:00:55 [SERVER] [INFO] Saving chunks for level 'testing'/Nether
Client> 2013-05-10 16:00:55 [SERVER] [INFO] Saving chunks for level 'testing'/The End
Client> Invalid memory access of location 0x0 rip=0x11ec75460
Client>
Game ended with bad state (exit code 139)
Deleting /Users/Isaac/Library/Application Support/minecraft/versions/13w19a/13w19a-natives-1368215968968554000
In a very similar bug strange things happen to slime block rendering depending on position