Often Zoneminder users experience problems with cameras being displayed over multiple inputs. This is typically found on cards that share (multiplex) BT878 chips. To solve this problem set MAX_FPS to a low number, typically a number between 2 and 5 on each video monitor inside Zoneminder. 

Note: When sharing ports all shared ports have to be the same resolution / color palette. 

Then change CAPTURES_PER_FRAME in the options menu to 2.