Save the state of the trader offer until you make a trade or the trader departs. In vanilla the trader offer window resets any time you switch tabs or close the window.

Changelog

-v1.0.0 - initial release

-v1.0.1 - Removed the saving of trade offer for Wandering Merchant Hermit that you find in small glades because it was causing some bugginess with the Trading Post Merchant.