Huh. It's always worked that way (equip previous pants) for me. Although, I can't say I have ever done it via the Relay Browser; a simple "breakfast" in the CLI will get all of the day's clovers for me.
Ah, I've only used the relay for clovers. Here's what it has in the gcli when i click fish for worthless item:
Pulling items from storage...
Putting on Travoltan trousers...
Equipment changed.
Purchasing chewing gum on a string (1 @ 47)...
You spent 47 Meat
You acquire an item: chewing gum on a string
Purchases complete.
Using 1 chewing gum on a string...
You acquire an item: worthless trinket
Finished using 1 chewing gum on a string.
Then it keeps the pants on