> FWIW, there's no need to set DRI_PRIME for steam itself, it can be set in Properties -> Launch Options of individual games.
Then I have to don't forget to set it for every game. Set it for Steam once is
easier.

> Does the problem still occur with a current kernel?
Due to few issues with Linux 4.9 (not related to graphics) I tested this with
Linux 4.8 and Mesa 13.0.2. Yes, issue is still reproducible.