Magma Cubes spawn in too small spaces (smaller than 3 x 2.1 x 3 block)

Magma cubes can spawn spaces they'd suffocate in. Video file too large, so here's the upload:

https://youtu.be/M_J0RXSw2dg (removed due to duplicate issue)

 

Note: The magma cubes on top did NOT spawn on the glass, they spawned through it and jumped up.