We take into consideration few things here:
1) What is someone abuses the merit system with a hacked account. If the original member gets account back, will he get those merits back to spend on quality posts.
2) If someone did this one day after the merit system, it is possible he might be testing. How will such cases be differentiated from abusers.
1. I don't recall reading about these kind of post, but i don't think the original member would get back the abused merit.
2. I don't think it would be hard to differentiate an abuser to not. Who would try and test to give out 50 merits at a single post? Only abusers would do that right? Unless the OP made a very well written posts which he deserve the 50 merits for it, that i think, is acceptable.