The configuration schema for the "winrules" plugin sets an arbitrary maximum width and height for window sizes to 4096 pixels. This limitation was introduced in git commit 3bf4bb10c34284d0a6dc1fd8e51c5991074d3c06 (circa 2010). With standardized display resolutions that exceed 4096 pixels, and the prevalence of multiple-display setups, this limit makes a lot less sense than it did in 2010. It's hard to pick a good value for a maximum here, as anything reasonable has the chance of very quickly becoming restrictive. We could just as well remove the maximum altogether and CCSM would be perfectly happy. I've chosen to use another arbitrary, but notably higher, limit in the attached patch.
This issue was discovered while trying to use winrules to work around a window size bug in a game (Cities: Skylines) which was thoroughly convinced its window was the full 5760 pixels of my display setup, but had only managed to get a 1920x1080 window. Normally I would consider this sort of thing to be too frivolous to report, but I used to be much more active in Compiz development several years ago and was interested in seeing what the community looked like these days.
As an aside, I believe Sam chose 4096 as it was an incredibly common maximum texture width/height in high-end GPUs at the time - we simply couldn't support wider windows.