A couple weeks ago I was tidying up the tagging of glacier-related questions on Earth Sciences SE.
The number of questions with the [glaciology] tag is currently 102 according to the search result count:
However, when I check the question count for the tag it says it has only 85 questions:
This number is relevant because it establishes the order tags show up in the tag list and also determines tag eligibility for tag badges.
The discrepancy between 102 and 85 questions seems to arise from 17 questions with the tag [glacier] that is a synonym of [glaciology]:
However, there seems to be a bug here as well. Because 14 of those 17 questions tagged [glacier] are ALSO tagged [glaciology], the question count for [glaciology] should then be 99, not 85. It seems that a question tagged with a tag does not increase the question count for that tag if also a synonym of it is tagged.
I checked the numbers above by scrolling through all the returned questions, but @Rene provided an nice SEDE query providing the same values, and also the baffling result that all questions seem there to add up to 87, while a search of the [glaciology] tag throws 102 results as shown in the first image above.
To make this even more confusing, if you go trough all those 102 questions, it turns out that there are only 90 of them. If you set it to display 15 questions per page, the first two pages have 15, the third have only 13, the fourth, fifth and sixth pages have 12 and the last page have 11 questions. All this questions add up to a total of only 90 (87 with the [glaciology] tag, plus 3 with the [glacier] tag only). If not a bug, there is something very weird going on here.
In any case: Shouldn't the question count and tag badge eligibility consider all the questions with the tag AND its synonyms?