Deleting a Contact breaks ModComments in Trouble Tickets

See attached screenshot. A customer reported that on a particular Ticket the were unable to add or view any comments. After a bit of digging it turns out that one of the comments had been added by a Contact. This Contact had then been deleted (but fortunately was still in the recycle bin).

This is very poor IMHO and renders the ticket unusable - you cannot add any new comments or see any old ones...