Sneak Off Soul Sand

If there is a block perpendicular to a soul sand you are able to sneak off it. This is the same with the corners of block. I expected if I sneaked on a soul sand with a block perpendicular it would keep me on the soul sand. Instead I just normally sneaked onto the perpendicular block as if it were the same level. Is this because soul sand is slightly shorter than the other block

Steps to reproduce:

Place A Soul Sand
Destroy One/Two Of The Perpendicular Blocks
Sneak While On The Soul Sand And (Still Sneaking) Walk Towards The Edge With A Perpendicular Blocks. You Will Slip Off.
Repeat But This Time Where There Is No Perpendicular Block. This Will Not Happen