Request: Library: Collapse (All) Groups / Folders

[NessFreaK]

By default, all groups / folders / albums are expanded. There doesn't seem to be a way to collapse them? The arrow highlighted doesn't seem to function.

Depending on sorting method, there can be several hundred groups (ex: when sorting by artist), which can take a very long time to scroll through a cumbersome list. I'd like to be able to either collapse them all on command, or have them all start collapsed by default.