<M--> and <M-+> not working

[electricWah]

Control:
5é*
Count of 5, prints 5 asterisks
https://tio.run/##K/v/3/TwSq3////rlgEA

With :
5<M-->é*
Count of 5, decrement the count by 1 to get 4, but it only prints 1 asterisk
https://tio.run/##K/v/39TGV1fX7vBKrf///@uWAQA

Same thing with <M-+>:
5<M-+>é*
Count of 5, increment the count by 1 to 6, but it only prints 1 asterisk
https://tio.run/##K/v/39TGV1fb7vBKrf///@uWAQA

I tried testing with the actual character rather than the verbose mode, but it seems that the given character for on the wiki is just a regular - character. I tried that, and an "–" (em dash), and I'm still not sure which is correct but both had the same effect anyways. I also tried « for <M-+>, no difference either. It seems that the command is using up the count so the next command can't use it. I don't think this is intended behavior, as it wouldn't be a very useful command.