Factorio Forums

when I pick up an item from my main inventory to my cursor, on_player_main_inventory_changed fires (good)
ditto when I drop an item to my main inventory from my cursor

when I pick up an item from my quickbar to my cursor, on_player_quickbar_inventory_changed fires (good) and then on_player_main_inventory_changed fires (bad)
ditto when I drop an item to my quickbar from my cursor

Thanks for the report. It's fixed now for the next version of 0.15.