You implied it here:

>Strong desire to work on a specific piece of the code (or to not work on one) might even in some cases be a red flag.

I understand an engineer should compromise. But if you want to specialize in high performance computing and you're pigeonholed into 6 months of front end web, I can understand the frustration. They need to consider their career too. It's too easy for the manager to ignore you of you don't stand up for yourself. Some even count on it and plan around the turnover.

Of course, if they want nothing other than kernel programming as a junior and you simply need some easy but important work done for a month, it can be unreasonable. There needs to be a balance as a team.