Not sure whether this is a bug or a reputation level problem, but I noticed that there's a tag "filter" and a tag "filters", which I suggest should be merged to "filters". However, all tag modifications are read-only for me.
The easy way is to simply retag the applicable questions. There are only three of them...
On beta sites, you need 1250 reputation points to create tag synonyms. Since it'll be a little bit before anyone hits that, you can just ask a moderator (by posting here on meta) to set one up for you when needed.