This same thing has recently happened to me. I have successfully traded scrolls on the market once before this.
I play using the PlariumPlay app for PC. The game runs better this way than by running through a browser.
The scroll trade was and extra smuggling duplicate (#5?) to be traded for Smuggling #2.
The caravans dispatched and showed progress as before.
I did get the 2 msg from the herald, one telling of the successful delivery of the scroll I sent, the other of the successful receipt of the inbound scroll.
deleted the herald's messages.
Went to Lost Arts (to get other studies started) and saw Smuggling at 3/6, should have been 4/6.
Went to house of scrolls and verified there was indeed only Smuggling 1, 3 & 5 as before the trade except qty was only 1 of each.
My caravan was still returning from this delivery of the scroll I traded off.
Edit: Should I submit this as a new issue or is this an appropriate addendum?