Custom generated qch files with stylesheets defined do not render properly since Qt Creator 3.6.1. For testing I tried the V-Play documentation build both on Qt Creator 3.6.0 (left window) and 2.6.1 (right window), see the attached screenshot. The qch file is the very same, so I suppose it's not a configuration issue during doc creation.
Also, the Qt docsets look kind of broken (see second screenshot attached).
Tested on Mac OS X and Windows with the latest builds from the Qt SDK and standalone versions. As there was a possible issue with a wrong mirror I also had a look at the Mac OS X build, which is:
Qt Creator 3.6.1
Based on Qt 5.6.0 (Clang 7.0 (Apple), 64 bit)
Built on Mar 14 2016 09:38:07
From revision 53b8ca08bf