As challah bread expands quite a lot while baking, this isn't unusual. If you notice this occurring while baking, you can cut the top threads of the twine and this should lessen the bread expanding disproportionately out one side. This often results from the bread being underproofed or too tightly shaped. The benefit for these buns is that pumpkins (being natural) are not perfect! The bread will still be impressively shaped and delicious!