I've never had an issue with the inventory system.
As a best practice I send all me "sellable" items to on character. Usually whoever can carry the most.
I let them do all the buying/selling, and then anything they buy for other party members, I transfer over once I've left the vendor.
I have 1 character keep most/all quest realted items and readable materials. 1 takes all the crafting stuff.
Never had issues with this method.
