When you drag an element with the v-drag attribute everything works fine until the cursor (not the element) touches the left side or top side of the document. When that happens, the following exception is raised:

When the cursor is touching the top (or beyond it), dragging does continue to work, but when the cursor is touching the left side, the position of the element stops updating until the cursor moves back into the document.

I would guess that the fault lies within these lines:

Where e.touches is undefined.