Hi Sebastiaan

Sorry for this reopening, I'm not sure if you saw my final comment after marking your previous answer as correct, which was not, and I was not able to removed it as correct.

This is the case: https://our.umbraco.com/forum/umbraco-8/96317-multinode-tree-picker-selected-checkmarks

I've discovered the 'bug'

Apparently, when your doc type as an associated ListView and it's used in the MultiNode picker, when selecting the item it's not displaying the checked mark as it's doing it on the standard view.