I noticed this when a correction was made to some blocks not being stored and implemented correctly. (A previous report of mine, actually.)
The problem you describe is double-edged. I personally want to block something immediately and scrub it completely from my existing feed. The refresh is welcomed in my case as there might be multiple posts from the same community or user.
This probably requires a feed refresh for multiple reasons. The first I can think of is for performance and the second reason is likely for code complexity and CPU cycle reduction.
I would vote to add a menu opinion to purge and refresh the feed after a block since I can see the advantages and disadvantages to both settings.