I was cleaning up CMake build script for a project and noticed .h were listed in SOURCES of a target. As CMake ignores header files there, I decided to remove them. But apparently, that causes the header files to not be listed in the project sidebar.

Qt Creator should probably do what CMake does and use "GCC's -MD and -MF options (and the equivalents for other compilers), which spits out the header dependency information" rather than rely on headers listed in sources.