The Dwarven Thrower magical item can't be thrown. It doesn't have the "thrown" property. This seems odd...
+1 Arrows don't deal extra damage. I tested them with a +1 bow and a normal bow.
Gauntlets of Ogre Power Str 20: I initially had them equipped on my Hill Dwarf when his strength was 17. Then I leveled up, increasing his Strength by 1 point (while still equipped/attuned to the Gauntlets). Afterwards, the Gauntlets set my strength to 20. This persisted even after de- and re-equipping them (de-equipping them returned my strength to 18). A quick search of the forums shows that other people have had similar issues (str set to 20), but not exactly the same as my situation.
Edit: I was mistaken, and it is the Leather Armor +2 stocked by Joriel Foxeye that is the same as a +1 leather armor, not a greatsword +2.
v0.5.42. Apologies if any of these are known issues. I'll echo that the Dwarven Plate also doesn't visually appear on my (Hill Dwarf) character.