The description of the function FcConfigUptoDate states: "Checks all of the files related to config and returns whether the in-memory version is in sync with the disk version". So, when the in-memory version of the configuration is changed the function should return FcFalse.
However, the implementation of the function FcConfigUptoDate returns FcTrue in this condition.
The detailed bug description can be found at:
Updated documentation to reflect that this function only checks file timestamps against when the configuration was created, not when any other changes were made.