Unless I'm missing something, the filter bar doesn't seem to work on folders when flat/mixed mode is on.
In case that's relevant, my filter bar is in regex mode.
The filtering does work on files.
Attaching a video.
FindThis.zip (4.29 MB)
I guess you're missing the "Filter folders in Flat View" option 
Make sure you understand what it does before turning it on. ALL files and folders below non-matching folders will also be filtered out, not just the folders themselves.
