[QUOTE=Laura]Monitor 1: 800x600 mix of layers 1-3 w/fx
Monitor 2: 1024x768 sep. no fx

/QUOTE]

suggest you set both monitors to the same resolution- this was part of the problem after 10.3.5

try both monitors set to 800x600 and then both monitors set to 1024x768.
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do not use the catalyst gui to do this.
make sure that catalyst is not set to change the screen size at startup of catalyst-

quit catalyst and set these display resolutions to be the same on both monitors using the system preferences - then as an extra precaution reboot the computer.
repeat at other resolution.

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the problem is potentially related to issues that 1024x768 and 800x600 do not run at the exact same frequency - you would think they both run at 60.00HZ - . No they dont. at 1024x768 the display runs at 60.02Hz, and at 800x600 the display runs at something like 59.97Hz.
Very confusing, but this can and doees affect the performance of catalyst, which gets very confused by the slightly different refresh rates on each monitor