Today, I got this 3-year-old question in my rss feed: Is it glitching?
Sigh; yes, that's probably me; I've disabled the smoke-test server related to this while I investigate. Almost certainly the same bug as this, manifesting in a slightly different way. Both look very-much like the wrong offsets being applied to a pre-indexed chunk'o'data. For you it meant you got slightly the wrong page of records; for other folks it has meant the wrong tag entirely - but the per-tag pre-indexes are stacked adjacently, so that's actually the same thing... ish.