The following logs from the synergy server prove my estimate of pixel 1200 was precise :-) and that the client actually sent wrong geometry data to the server: BAD client (synergy 1.8.7): [2017-02-05T20:51:56] DEBUG: received client "apollon.mittagstun.de" info shape=0,0 1200x1920 at 540,960 GOOD client (synergy 1.8.2): [2017-02-05T21:03:24] DEBUG: received client "apollon.mittagstun.de" info shape=0,0 4080x1920 at 540,960