Biggest raidsize is 25! (there's just not anoth space for 40 ) When you join a bigger raid, the panel gets mezzed up.
Grid needs some configuration to fit into the panel.
Goto the Grid Options and then to "Layout"
Grid should be "locked" to prevent unwanted movement.
Grid borderdistance should be reduced to 4
scaling should be reduced to at least 80% better 75% (on my screen)
Seams since Patch 4.0.3 the scaling of Grid is no longer needed. YAY! ;-)