The ling on the bottom start location can go inside the base but not outside. Tried with CC also but that was solid wall.
I was researching how walls could be built on this map when i found this. I thought it was ling tight first, but when trying from outside to in it was not :'D
As most of you may know, this page: List of Unit and Building Sizes is used to check whether buildings to buildings are solid wall, however there is no such info vs doodads/terrain.
Fun fact from this is that you have to check your walls on new maps from both directions :D
Some one found the same kind of bug on La Mancha a while ago:
(the bugfixed version I made for BWCL fixes this)
I investigated it and came to the conclusion that it is an issue with BroodWar's short range pathfinding and how it evaluates obstacles. The gap is wide enough for the Ling to path, but short range pathfinding does not necessarily always recognize the right moves to get the Ling to the gap. You can still get Zerglings through, without too much of a hassle. All you need to do is click a short distance in front of the gap at the side you the Ling's coming from, so it gets into a position where it can easily reach the gap, then click a short distance past the obstacle, and the Zergling will quite handily pass through.
Pictures from the Editor (with unwalkable terrain and collision boxes visible):