Maybe we should file an enhancement bug to improve error reporting foropDispatch.
I found this https://issues.dlang.org/show_bug.cgi?id=8387 and cast a vote for it.I've cast a few votes in the bugtracker, don't know if that raises the visibility of the bugs or what. Maybe not since this bug had 4 votes to begin with and has been around since 2012... or maybe 4 is not that many.