It's a few years ago now, but upset me a lot at the time and I don't want to repeat the mistakes.
I had a reasonably senior post and an excellent assistant. She was very efficient and keen to learn, so I used to look for opportunities to train her in aspects of my work, and give her some additional responsibilities, thinking she'd be a good replacement when I moved on. She told me she was keen for this. I also arranged for her to do a qualification, paid for by the organisation, which would facilitate that, which is what she said she wanted. She excelled at that.
I always felt that I was supporting her development whist retaining overall responsibility and on the odd occasion when something went wrong because I'd let her step up, I always completely owned that.
Then I had a period of absence following a bereavement and she was brilliant. Both I and my boss thanked her over and over for how she covered for me, although it was always clear that whilst she did the leg work, boss was the one responsible during that time.
When I returned to work, still struggling, she was very reluctant to hand a lot of things back. Some things I put my foot down and took back, but as I was still not myself, I let her carry on with others, and was very grateful, which again is what she said she wanted for career development.
After a while she complained to my boss that she was "carrying" me. Which was probably true, but also shocked me because I'd been asking weekly if she was OK and what she wanted me to take back.
When I talked to her about it, she said boss had got the wrong end of the stick and everything was fine.
Then I heard she was saying the same to other staff members (also my line reports) too and all of a sudden I felt like I'd lost the dressing room, when previously all feedback had been that I was a respected and supportive manager.
Anyway that, plus feeling I needed a new start, was the motivation for finding a new job, which I did quite quickly, but she didn't apply ro replace me and, so my old boss tells me, she's still complaining about doing work she doesn't think she's paid for under he new manager.