From the 25.0 Patch Notes:
[Mercenaries] Fixed a bug where completing a Heroic Bounty would not count for Tasks requiring a Normal Bounty completion.
All the difference I see is that now such Visitor tasks explicitly specify ‘Normal’, and completing it on Heroic still doesn’t count. You call that ‘fixed’? 
Or was it only for other tasks, such as story ones or those from time-limited events that had such problems (for example, [Mercs] C'Thun task 5 not completed on Heroic)?
PS See also: Mercenaries: Visitor tasks not completed on heroic (25.0) .