Mesh opens at the back Being relatively new to Blender and 3D modelling in general, I recently made a low-poly female character using video tutorials by PXstriker (Linked below). The model itself is made using the mirror modifier, as to only need half the work.

After I started rigging and posing this model, I noticed that the model rips open at the back, particularly near the legs. Whether the mirror modifier is applied to the mesh or not doesn't seem to make a difference.

Is this a normal problem using the mirror? I've looked around google and other tutorial sites, but nothing similar to the problem seems to be mentioned.

YouTube Channel Link: https://www.youtube.com/user/PXstriker/videos

Front view of the model:



Back view of the model, mesh is visibly opened whenever the legs are posed:
As said in the comments, mirror modifier has to be 1st in the list (up), if it's not, click on the up arrow at the upper right corner of the mirror modifier. Be sure to check "merge" and "clipping" options.

If the problem still appears, edit your mesh, select all vertices that should be in the center. Scale them to zero (align) on the X axis (S X 0), then move them on X axis to make them stick (G X -move mouse-) repeat this on the other X direction (G X -move mouse to the other direction-). All center vertices should now be in the center, clipped and merged and will move with the armature as they should.