In details view, select a few folders in the current folder, either by dragging over them, or by selecting one and using shift+arrow keys.  (Don't select the first listed folder.)  Now, click the ">" at the left of one of the selected folders.  Now, suddenly, all the folders above the folders you selected are now selected, too.

I reproduced this in my home directory several times using several combinations of folders, but upon closing dolphin and reopening it, I can't reproduce it anymore.

Reproducible: Sometimes