When using the fr-be-azerty remote keyboard layout on an RDP connection, the dash ('-') and underscore ('_') are swapped.
As documented on Wikipedia, the underscore should be passed when using shift, while the dash should be passed when not using shift. The actual behaviour is reversed.
I've written a simple patch for fr_be_azerty.keymap that fixes this (see attached patch file). I've also compiled and deployed guacamole-server with this patch to fix the behaviour on my installs.