When exploring, I found that i couldn't pick up more stuff. This is a pretty common occurence, since I've been saving up for a warehouse upgrade.

I went over to my inventory and put some stuff up for sale, and it disappeared from my inventory as usual, but when I returned to the explore tab, I still couldn't pick up the item. I figured there was some sort of glitch that had given me too many items, and tried to sell some more stuff. I repeated this process several times until I realized that there might be a different kind of bug. I counted the number of items in my inventory, and there were 22 in total. Despite this, my inventory showed 30/30 and I still can't pick up items.

The items in sales are still stored in your warehouse until someone buys them. 

Ah, that makes sense. I didn't see them, so I assumed they weren't stored there. Thansk for letting me know!

No problem! :)