Sometimes I am working on a scene, do something in the viewport and instead of having me switch to select mode, I keep stuck in “drag mode” (the one with the hand icon as mose cursor where you can position your camera). This often happens after switching from orthogonal to perspectiveview.

Anyone else ever experienced that or knows a workaround?

Yep,

Something similar, I experience it on my Mac pro. If I'm moving around in the network view and afterwards for instance I would like to pan around in the persective view but the focus stays at the network view while I'm working in the perspective view.
My work around is to move around in the network view and than the focus normaly let go.

I find it hard to explain it properly so I hope you'll get the cluw. ;-)