Stupid me though they would pin the folder tree open but as far as I can see they do nothing except reset when the app is reopened.
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Pins keep tree branches expanded.
They are only temporary unless you save them.
Settings > Set Lister Defaults, if you want to save the current pin states into the Default Lister.
(Or, if you're using a layout, save over that layout. You can also load and save the pin and expansion states of the tree into named presets if you need different things at different times.)
OK, there is a bug in pinning and that is why I couldn't understand it. It doesn't work if you pin a subfolder, you have to pin the whole path to the one you want pinned. Also documenting pinning would be nice. I'm currently using the beta.
Where do I report this bug?
This is the right place to report that bug, giving a short description. Unless it's a crash, where you would submit the crash report, like in this link.