Qt-Creator: keyword "constexpr" not accessible via F1 in cppreference

Hi everyone,
I use Qt Creator 13.0.0. and have included the file cppreference-doc-en-cpp.qch. So if I put the cursor on a keyword (e.g. const) in the editor and press F1, the corresponding information from cppreference-doc-en-cpp.qch appears. If I use constexpr instead and do the same thing, Qt Creator tells me that there is no documentation for it. That is of course wrong, because if I open cppreference-doc-en-cpp.qch (without F1), the keyword constexpr can be found there with the corresponding information.
Questions: Is this a (known?) bug? Is there a solution?
I posted this some times ago in Qt-forums, but unfortenately without answers
Thanks for answers