While I've made use of title and domain filters for a few weeks now to filter out unwanted posts from communities I otherwise don't want to block, I noticed today that if you press the 'Add Filter' button for Title, Domain, Community Name, or Username filters, but leave the filter blank, all posts will be hidden.
In the case of Domain filters, oddly up to three recent non-URL posts seem to be able to appear when a Domain filter is blanked out, but not all non-URL posts in general.
For some reason, the same problem doesn't seem to occur when blanking out a Content filter, as far as I can tell.
Here's is a demonstration of the glitch, using a blank Community Name filter:
