If you use SQL comments in a report, runtime parameters are not fully ignored. For example: /* WHERE branchcode = <<Library|branches>> */ When the report runs, it correctly ignores this parameter, but it still requires the a library branch to be selected before the report can run.
I noticed this yesterday as well. Unfortunately, I can't really think of a solution for this, since we don't have a SQL parser in Koha. There's no robust way of knowing the runtime parameter, which is a Koha only non-SQL concept, is in a comment or not.