To a certain extent I am thinking strategically. There are roughly 3 aspects to a Zeugnis/Zwischenzeugnis:
1)Getting it.
2)Content.
3)Presenting it to a prospective employer.
3 is the most important one, to my mind. If you have one which is neutral, or not exactly glowing, you will be asked to explain. If you can say "shortly before they fired me I asked for a Zwischenzeugnis after 3 years of employment, and this is what they provided" you are in a better position than saying "it was a crap company and the boss was an idiot". In both cases you are making the same inference, but the former is much less contentious.
For example, it may state; "Employee X sometimes goes beyond his scope of his/her responsibilities to ensure success for his team and company". The receiving end may ask why this only occurs sometimes . Whereas it would be better to omit sometimes , or ask them to replace it with always .
HR should give the employee a proof for approval to catch such things.
If I write a reference for someone that's what they get like it or not. If they are an outstanding employee then there might be an option to adjust some things.
Herr Ueli Whinesalot was employed from the period X to Y in the position of Senior Time Card Puncher. This guy walks on water and I weep* as I write this letter of recommendation on the occasion of his leaving. There will never be another employee like Ueli and I'm probably going to have to hire 3 people to compensate for the work he did (to us) . Ueli will never fail to make an impression and I strongly recommend you load him up and give him as much work as humanly possible. You will be amazed at the response.
*for joy
The funny side of the story is that the problems started when I showed my proposal for the new generation of devices. They didn't believe it would work and it worked and they were ficked up in some way...... I made suddenly two enemies without knowing it (one of them the team leader).
I never had such a situation because of being creative and good in my job. I was too naive and let the ball get bigger against me...
As said, always too sides. There was just another thread on someone who thought he was more amazing at his job than essentially anyone before him ever, whereas his employer very clearly completely disagreed. Again, not saying that's necessarily the case here, but sometimes a little digging into why someone changes their behaviour towards you as well as how you yourself may have contributed to it (even if not consciously) doesn't hurt.
I am not going to fight or something. I will quit in a month with a new job and we're friends... they lose much more than me. The only thing that ficks me is that they are going to register some patents of my work with the name of some bastard that don't even understand how it works. Anyway I am sure they will pay someday for the bad ethics.