Hey I have been racking my brain for ages trying to figure out a way if how I can get around this problem but I just cant get around it so I thought Id try my luck here. Im making a very low poly game character. Ive rigged it up and everything and am now playing with the paint weights tool on the legs. However when im trying to clean the area around the crotch this always happens: 
I try and place the verts back into place using the move tool but it seems that its locked for some reason or another. I have checked to see that the verts are all merged and they are so im not quite sure what the problem is, any help would be greatly appreciated 
Note: it also does the same thing for the other leg just the mirror image of whats happening on the right leg.