If you activate a catalyst next to a sideways deepslate block (not cobbled) sculk doesn't grow over it

How to reproduce:

1. Get a catalyst and deepslate block
2. Place the deepslate sideways and the catalyst next to it
3. Spawn a mob and kill it
4. Check if the sculk spread

Observed Results:
Sculk doesn't spread.

Expected Results:
Sculk should spread.