Problem
It isn't obvious to users that a filter is applied to a layer if they have collapsed the drawer e.g:

Filter applied:

Filter applied, drawer collapsed:

The same issue applies to the multi-filter panel - a user may have closed the model after applying a filter, and not realise a filter has been applied when looking at the layer.

Proposed Solution
A visual cue should inform the user that the layer is filtered (meaning they are only seeing a subset of data)