[CMake] add_custom_command weirdness

[Christoph Höger]

Hi all,

I have a buildsystem here for a project containing several subprojects. All those subprojects have their own CMakeLists.txt in a subfolder.
One of those subprojects needs to run a script to generate some sourcefiles:

add_custom_command(OUTPUT ${typesh} ${typesc} 
	COMMAND ${binbash} ${PROJECT_SOURCE_DIR}/mosilac/mktypes.sh
	DEPENDS ${src}/hcparser.y
	WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}/mosilac)

This does work. As it does in other places. But in that single place I have a problem when working on other parts of the buildsystem: 
Whenever I change a CMakeLists.txt file subsequent make calls lead to a re-generation of the output files, although they're unchanged.

Does anyone know why this happens?