The common surface implementation used within guacamole-server is incorrect with respect to binary transfer functions as of
GUACAMOLE-188, which added support for the alpha channel to the common surface.
- GUAC_TRANSFER_BINARY_SRC (alpha channel becomes a copy of source)
- GUAC_TRANSFER_BINARY_NSRC (alpha channel becomes a copy of source and is NOT INVERTED)
In all other cases, the alpha channel of the destination is preserved.
The common surface must be modified to duplicate this behavior.