> Currently there is a bug where the prefix arg changed for the repeatable
> commands, is applied to the next non-repeatable command.  For example:
>
>   C-- C-x o o C-n
> or
>   C-x o C-- o C-n

Actually, this too confusing feature that allows changing prefix args
during the repeating sequence increases code complexity enormously.
For posterity I'll leave here the patch that completely supports it.
But this feature will be removed (unless someone will ask to leave it):

  C-x } }  C-1 C-2 } }  C-3 C-4 } }

Only this will remain:

  C-x } }  C-1 C-2 C-x } }  C-3 C-4 C-x } }