Apparently this method is only used by the transaction details dialog, the csv export and the "copy address" context menu entry. The background for the appended thing: If you create a transaction to two recipients (using sendmany or the "add recipient" button in the send tab), this transaction is displayed as two different transactions in the history tab. To make the id unique again, the number of the output is appended in the table mode. For example, one part would show the (Sub)TxId 2c775dbacf61a0ec59b40a2da414fa21a3a0cc74727c52d2459e7772a3316725-000 and the other 2c775dbacf61a0ec59b40a2da414fa21a3a0cc74727c52d2459e7772a3316725-001.

I'd suggest to extend the tablemodel to add a RawTxIDRole which returns the TxId without that additional subId.