While noodling around with TracXMLRPC, I discovered that if ticket X has populated fields 'blocks' and/or 'blocked by', and the tickets referred to in those fields doesn't exist, then when I attempt to view ticket X, trac reports
Error: Invalid ticket number
Ticket 93 does not exist.
Where 93, in this case, was in the blocks field. Ticket X is now completely unavailable, even to TRAC_ADMIN, unless you poke around in the db and remove the offending ticket numbers.
Would it be a better idea if MasterTickets reported that the referred tickets are invalid - perhaps by unWiki'ing the ticket numbers, or striking them through - but allow you to view or edit ticket X?