CC Cas Glitch

Hi. This is a problem with weights.
Select right trouser leg either in UV Editor ( with Keep UV and Edit mode mesh selection in sync ( 1 ) ) or in 3d view ( with Limit selection to visible off ( 2 ) ).

Enable Show Weights ( 1 ), click on + and type in calf ( 2 ), choose b__L_Calf__ ( 3 ), click remove button ( 4 ) to clear selected area from that group. Repeat for b__L_Foot__ and b__L_Thigh__.

Then press Ctrl I to inverse selection and repeat the same for b__R_Calf__, b__R_Foot__, b__R_Thigh__.
Switch to Weight Paint mode and click Normalize all ( 1 ). If the areas where you removed vertex groups had weights from the right groups, they will be normalized automatically. If not, you can enable Face Selection masking for painting ( 2 ) and using Blur brush ( 3 ) just run ( 4 ) through these areas with the right groups selected ( 5 ). It should normalize itself if Auto Normalize is enabled.