Neither the keybind nor clicking on the arrow button will cause the GUI to move, you always need to do it from your personal inventory.

I suspect this has to do with how you're doing the check in attached_gui_open (line 216), you probably want to compare against LuaPlayer::opened instead of player.gui.

Read that entry carefully, it does not provide a defines.relative_gui_type, but rather the LuaEntity object itself which has been opened.

It may be easier to entirely remove the attached_gui_open restriction.

Thanks, fixed in 0.4.3

The mod Inventory Trash Slot (0.4.3) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event inventory-trash-slot::toggle-trash-slot-keybind (ID 243)
__inventory-trash-slot__/control.lua:216: attempt to index field 'opened' (a nil value)
stack traceback:
    __inventory-trash-slot__/control.lua:216: in function 'attached_gui_open'
    __inventory-trash-slot__/control.lua:359: in function <__inventory-trash-slot__/control.lua:345>

When using the keybind with no GUI open in 0.4.3.

Changing line 216 to this seems to fix it.

if player.opened and player.opened.type == def.type then

Fixed in 0.4.4.