If your primary loadouts are both using the same weapon, attempting to swap between the loadouts by pressing F will correctly change all of your other items, but lock you out of some inputs until you block or use a power.
Tested using two loadouts that both had the Scorching Twins equipped. Pressing F to swap loadouts would correctly adjust my hearts and other passive effects, but would make me unable to attack or sheath my weapon and also broke scroll wheel functionality in menus. Upon blocking or using any power, the input problem was fixed.
Trying the same thing out (swapping loadouts by pressing F) with a different weapon equipped in each loadout did not produce this bug.