I think there's a clear distinction in most jurisdictions between (c) and the other two.
Let's suppose this bug report really was written on company time, with company equipment, related to the company's business, so we don't have to argue about how far-reaching your employer's rights should be here.
In (a) and (b), you've provided services to the code maintainers. Perhaps your employment contract forbids you from doing that, just as it might prohibit you doing project management or fixing their plumbing. But the recipient of those services hasn't done anything wrong.
In (c) you've additionally created intellectual property, to which you have some rights, including copyright. The code maintainers can't use that code in their product unless you assign them certain of those rights (or unless they can avail of other exemptions like fair use). But those rights might not be yours to assign - they might be your employer's. In addition to you potentially breaking your agreement with your employer, anyone republishing this code may be infringing your employer's IP rights (maybe under good faith, maybe you indemnified them... But still your employer has a legitimate complaint).
Let's suppose this bug report really was written on company time, with company equipment, related to the company's business, so we don't have to argue about how far-reaching your employer's rights should be here.
In (a) and (b), you've provided services to the code maintainers. Perhaps your employment contract forbids you from doing that, just as it might prohibit you doing project management or fixing their plumbing. But the recipient of those services hasn't done anything wrong.
In (c) you've additionally created intellectual property, to which you have some rights, including copyright. The code maintainers can't use that code in their product unless you assign them certain of those rights (or unless they can avail of other exemptions like fair use). But those rights might not be yours to assign - they might be your employer's. In addition to you potentially breaking your agreement with your employer, anyone republishing this code may be infringing your employer's IP rights (maybe under good faith, maybe you indemnified them... But still your employer has a legitimate complaint).