Every time you speak to an NPC, the gifting present particle effect plays as well as the present model changing. This happens every time I speak to the NPC. The list of NPC’s that do this are:
-Circuit Central
-Rob’s Imports
-Sweet Suites
-DIY
-Songbirds
-Toystop
-Seasons
I have tested this with as many NPCs as I can find but those are the only ones that seem to have the bug