RemoteFrameBuffer in 3.8 - unknown rect encoding -240

When running the RFBserver in a Full 3.8 image, I receive the following
error when running vncviewer on Linux:

Unknown rect encoding -240

However, I tried the RFBclient in a Full 3.8 image to connect to said
RFBserver and it worked fine.
I couldn't find anything about this error except the C code -- which, I
admit might tell me a lot if I kept reading _all_ the code. (yuck) ...
but first:  Does anyone know what the error means (and save me reading
code...)?  ok.. ok... I'm a bit lazy... but, someone here might say.
HEY! You just have to do xyz and you're all set.

thanks,

brad