Well... I am level 19, about to be 20 and I spent all my skills on lvl 2 dmrs, lvl 4 sights, lvl 4 suppressors, bipods, and frag nades. That means I have used up all 19 levels if you count them. I have bipods on my spar 17, my MK-I EMR, and my Rahim, in my first three slots, but I noticed that I can no longer attach bipods to my other two slots which i have another spar 17 and another MK-I EMR. This is so even though I have unlocked them and I have them on my first three guns. To regain the ability to add these bipods, I will have to reset my tree and waste credits. Is anyone else having this problem?