Gaps occur in both meshes against the outer wall. Few other minor issues like some odd vertex colors.
Funnily enough the one gap is smack dab in your face when you load WhiterunPlainsDistrict01.
Affected Files:
<span style="font-family:courier new,courier,monospace;">/meshes/architecture/whiterun/wrterrain/WRShacksBase01.nif
<span style="font-family:courier new,courier,monospace;">/meshes/architecture/whiterun/wrterrain/WRShacksBase02.nif
<span style="font-size:12px;">Note: Both meshes are already included in USKP.
<img alt="" src="http://i.imgur.com/1sqaXBa.jpg" style="width: 780px; height: 1560px;" />