The lack of highlighting is to be expected given that you're essentially browsing by tag (though multiple ones), and this recent change removed Interesting Tag highlighting on tag pages, for questions where the only Interesting Tags present are the ones which the tag page is for. Since you've stated that you've included all of your Interesting Tags in the query, none of the questions should be highlighted, since there are no non-queried Interesting Tags to use for highlighting.
So, the bug is really in the fact that you see any highlighting, and it comes from a fairly innocent mistake in the
appyPrefs() function which handles the question highlighting. This function iterates over your list of Interesting Tags to build a selector string to use in finding questions to highlight. It then takes the array of tags used to make up that "tag page" (which accidentally also contains the "or"s in this case, but that's not a huge issue) and removes them from the selector string so that they aren't highlighted per the feature change.
When it goes to remove the queried tags, it uses the following replace:
selector = selector.replace("div.t-" + tag, "");
In general this isn't an issue, but in the case of the C tag, things go a bit awry. You have several tags which begin with the letter C, and one of them must appear earlier on in the selector string that the actual
div.t-c entry. Since this isn't a global replace, one of the tag entries is cut off from the front (for example, a selector string of
div.t-cçç, div.t-c becomes
çç, div.t-c, where "ç" is the stand-in for "+" in the class names) instead of the actual C tag selector.
In the example, this effectively removes C++ from being highlighted, but since the C selector is still there questions tagged C will be inadvertently highlighted anyway. The replace should be more discriminatory about what it matches so that all of the correct tags will be removed from the selector string, which in this particular case would result in none of the questions being highlighted.