Wandering Trader interface immediately closes when Trader on slime block.

I set up some slimbe blocks near overhangs where villagers kept hurting themselves falling so I was ending up with dozens of Iron Golems - I carpeted them to make them look a little better. Wandering Trader spawned, I tried to trade - the window closed immediately with no interaction like a villager who had lost their workstation. Later, the Wandering Trader was away from the slime blocks, I was able to trade as normal. Curious, I waited until he was on the slime blocks again... and it happened again (immediately closing trade window) I suspect it's because of the ongoing status effect of slowing movement that slime blocks enforce.