This happens in survival mode also. When a block is placed in front of a painting, it forms a black out line and disappears(in creative) or pops out and can be recollected(in survival) <pictures below>
MCPE-4091
Painting can be sandwiched between two blocks in creative
Resolved
Cannot Reproduce
0
Water can also flow through a block occupied by a painting. The painting seems to be an entity but not occupy a block.