holding down mnemonic keys repeats 'activate' much slower than the key repeat rate

the motivation is https://bugs.documentfoundation.org/show_bug.cgi?id=142838 where a dialog has a "remove section" button with an R mnemonic

expected behaviour: You hold the ALt + R keys and it rips through removing sections very fast. actual behaviour: If you hold the Alt + R keys the sections are removed only slowly.