One of the characters that I am using, and only that one, has a unique problem. When I open his inventory he gets five tabs like just everyone else to allow the rapid switching of equipped weapons. With this one character, whatever I equip in tab one is always equipped in tab two as well. I've tried changing the item equiped in one tab and then switching to another tab, and then switching back, always with the same results. Seems strange to me.
Try unequipping all your weapons/ammo for all of your tabs, and re-equip them one at a time, make sure you have enough room in your inventory for the current weapon selection to fit in your inventory as the game unequips weapons before equipping other ones. Also I've noticed on occasion my weapon selection tabs are occasionally "forgotten" not sure if the game has a hard limit for the number of weapon selection tabs in memory or if it's just my machine that does this, but it happens. Fortunately you can swap your weapons around in combat as many times as you like without penalty if you have the quick draw feat, or at the cost of your movement phase without quick draw.
