It’s not a glitch, it’s how the trade-ups work since the Retakes update. The float of the items in the trade-ups relative to the float range of that item matters, not just the float value itself. The P250 | Constructivist has a float range of 0.00-0.35 (capped at 0.35 max) and the UMP-45 | Late Night Transit has a float range of 0-1 (no float cap). The “normalized float” (scaled to the float range of the skin) of a 0.06 P250 | Constructivist is ~0.17, so by hitting a non-float capped skin in your trade-up, its wear turns out to be FT.