S-75M3; Linebacker II; "Habu" flight...
After launching the first missile (missile guidance -method UPR; APP - method UPR) and Habu starts jamming, the lamp of tracking distance lit off, but still distance boresight is moving like in I-87T/T... Somethimes, when switch 150-75 mode it stops, sometimes not... I think, this is the same problem like Dvina "active guidance".

No. Just keeps the moving of the range bore-sight speed steady.

A question - what is the proper way to use RPK switch in SA-75M/MK Dvina?

Same with Volhov. Leave it at EKV.
If you want to frighten the enemy, you just flip it to ANT, and their RWR will light on "SAM Launch".

If you launch real missile, it will anyway internally override the switch setting.

At the Volhov with 75km and BR mode, it also internally override the switch setting.