I had not reached my limit; my blocklist currently contains only the four that I most recently attempted. We'll see if they remain there. I appreciate the user block tip though -- we'll see if that helps.
That's a common issue when saving settings in the interface, it automatically saves the first change you do and then ignores whatever you do in a short while (minutes). For instance, it's really annoying when I want to change the languages. One way to do it more quickly is going to each group (instead of using Settings) and directly press their page button.