Save to File defaults to rbxmx?

It’s happened with my friends as well (I’m on Windows 7, using SystemMenu if that’s important), whenever I right-click a model or selection, and then click “Save to file,” it always defaults to save as an XML (.rbxmx) file. Is there any reason for this?

Is this even fixable by roblox

Is there a behavior difference between rbxmx and rbxm?

.rbxmx is xml - and it’s huge.

.rbxm is ROBLOX’s propietary format.