steps to reproduce:
- acquire both melee weapons in your hotbar: here main is axe and "secondary" is machete
- proceed to select the secondary melee weapon via hotbar.
- now immediately switch to your main melee weapon again via hotbar. you can see how the secondary weapon suddenly replaces the axe in its main slot
- again select a different weapon (not the one currently in the main slot) or item (either by hotbar or otherwise)
the axe will be dropped on the floor if there is no space left in your backpack (likely) and the main slot is occupied