are you selling via the flea market, because that would be the only thing that would make it unselect the 1st item. You can sell multiple items directly to Reese, but flea market items go up one at a time because you pick the spot where they go.
im not sure what the difference is im pretty new to the game. i go in to recycling shop and sell to character in there
thats really all i can tell u im afraid...sorry
Well the flea market is where you can sell your items to other residents in the town. Your items appear on the blue platforms in the shop when you do this. You can either sell by pressing A at an empty blue platform or talking to Reese and selecting the 'flea market' option. You can only sell things one at a time this way.
The other option is just to sell directly to Reese for instant bells. Talk to Reese and select 'I want to sell' (I think) - this will then bring up your inventory and you should be able to select multiple items to sell.
Sometimes when I'm in a rush I go to talk to Reese but accidentally select the blue platform behind her instead, which brings up the flea market dialogue and not the normal sale dialogue - might be worth checking that you're not accidentally doing this!