Mutimeasure rest bar numbers

Searched for it in the handbook but couldn't come across any pictures or examples.
Bar numbers in multi measure rests have some unexpected behaviour, especially when a pickup measure is present in the score. (Number is off by one or displays the same number twice
Also the content of those numbers is a bit confusing to me as I don't understand what the "%" is doing in there.
What is the expected behaviour of this?