And it is nothing new. When I moved from GE to VD in 1988 I needed permission from both. And VD annotated the permit “Working in Vaud is prohibited” even though my B permit was locked to my employer in GE.
That's more than three decades ago, and predates not only the EU but most importantly the Bilaterale I+II as well as major changes in regulations on foreigners.
Things change, that makes a recent case all the more noteworthy.