Tags in blacklist are not matched as prefixes

The configuration form (and everywhere in the code) states that the string you enter in the blacklist are used as prefixes to match against tags:

The strings are matched as prefixes, so for example config: will match tags as config:core.extension and config:block_list.

But this is the code behind the matching:

if (strpos($tag, $prefix) !== FALSE) {
  $blacklisted = TRUE;
}

This code checks if the tag contains the blacklist value, instead of starts with it.
This should be changed to:

if (strpos($tag, $prefix) === 0) {
  $blacklisted = TRUE;
}