Managed to replicate after possessing an Archon and running myself into every wall. This is a result of the following:

• Any unit with flying can pass a solid wall
• This can only occur if the unit with flying is positioned above a chasm
• I.E. the unit is attempting to push through the wall from the chasm side

Jan has confirmed this occurs on levels other than C13. Tested with Archon & Bafu (Both floating and flying affected)

See videos: