For some reasons I still haven’t understood, the MIT-SHM extension pretends to work on a remote machine through a “ssh -X” connexion and thus isShmAvailable() in juce_linux_Windowing.cpp returns true, whereas it actually does not, since I get BadShm messages from X.
After some (painful !) investigations, I found out that these errors could be catched by testing the return value of untrapErrors(). Thus I changed the line
449 of juce_linux_Windowing.cpp (latest svn):
to
This seems to fix the problem.