Vines growing upwards to stairs

Vines groing upwards to stairs

What I expected to happen was...:
vines should only grow on non-full facades of blocks if they are growing downwards

What actually happened was...:
they grew on the non-full side of stairs which were above the vines

Steps to Reproduce:
1. Put vines on a block below stairs which are facing towards the vines
2. wait until the vines grow