My Hero screen is missing the alternate weapon slots for both regular and underwater weapons. At this time, only my lvl 30 Sylvari Elementalist has this problem (and I couldn’t find it anywhere as a known bug).
I believe the slots were available initially but disappeared somewhere pre-lvl 27. Pressing “,” doesn’t do a thing (i.e. she doesn’t swap to No Weapons or anything else) and dragging weapons to the empty spots where my alt-weapon slots Should be also proves fruitless.