"How does one forget in 3 months what they spent 2 years inventing and designing?" - BY BEING BETRAYED AND LIED TO. What about this? This is a repeating theme here: We betrayed our key personell, now they do not work as good as before we f**** them. Yeah, that is how it goes - he is looking for another job because promises not kept are making you guys garbage employers.

"I have no idea why they're apparently trying to provoke one of my top engineers and not explain why." - ah, you mean managers being stupid is not known to you? Simple like that.

You do realise that he is playing the game and hasn't actually forgotten everything after 3 months? I expect he sees you as part of 'management' even if you yourself know that you weren't in on what senior management did. "You should really assign those tasks to a chief engineer" - yes, now if only the company had one of those..

Does this answer your question? How can I deal with troublesome Professional Engineer?

This is a question that has at least two eerily similar questions about how people (badly) treat engineers - what do they expect? See workplace.stackexchange.com/q/145709/75821

I'm always amazed by these question, and not in a good way. "We screwed our employee and now he's not happy. Why?" - It should be fairly evident to you.

Please clarify: He asked to transfer teams for a year and you are trying to bring him back In 3 months. Does he want to come back to the old team in 3 months? Or ever?

Did you ask him if he wanted to return to your team after only three months?

this reads very much like a rehash of a recent popular question Departing senior engineer refuses to introduce replacement to open source community/peers

Its amazing how often companies perform pointless morale killing moves because they mistakenly think they hold all the cards.

So he did a lot of extra work outside the scope of his job description & regular hours, presumably in hopes of getting that promotion he was promised? He didn't get the promotion, but you apparently expect him to go on putting in all that extra work? WHY IS THIS EVEN A QUESTION?

@jamesqf .....*and* when he got transferred away from the original team to try and make his way in a new role, the OP dragged him back. (The actual sequence of events might not have been in precisely that order - but it would look like that to him.)

@seventyeightis, "You do realise that he is playing the game" probably ought to be "You do realise that he is polishing his resume, don't you?". The dude has been roylally shafted and owes the company nothing - except contempt.

Why is it so acceptable for software engineers to job hop?, except that he will not hop - your company pushed him

It warms my heart to see greedy and clueless management and bosses who don't stand up for their team members get what they deserve sniff. Happens not nearly often enough.

How come this question keeps popping up once in a while without being a duplicate? This is at least the 4th question of this kind that I see, and it seems to always follow the same pattern.

@Clockwork I suppose it keeps coming up because the same circumstances exist in many different companies. Enthusiastic and eager employee devotes significant time to the company above and beyond what they normally need to do, however once the job is done they aren't recognised as they feel they should. Unfortunately, this happens all the time. The Stack Exchange network has more technology related people visiting but the same pattern emerges in other fields, too. The sad truth is that management worldwide don't tend to care.

@VLAZ I think it is much worse. There was a clear promise by the management which was not fulfilled.

@lalala which is also quite ordinary. Happens everywhere. And I am not saying that's acceptable - it shouldn't happen. I'm just saying that it does. It's a common situation all over the world. I can't speak of the managerial decision process that goes behind this but it always seem to happen "further up". An employee is promised something and then it's not delivered. The arrangement is usually not official but an informal agreement.