Still an issue in v1.8.0 as of 12/20/18
The original mechanics of kelp in bedrock actually worked very well. If it grew into flowing water, it would break. If someone wanted to create a vertically taller source block column, you would place a kelp on top of the previous kelp. I would advocate for a return to that mechanic.
This is still happening in v1.7, v1.7.1, and v1.8 on Bedrock. We also play on a Realms, but as of 12/13/18 this is still a serious issue. It happens on multiple portals on our realm. Some of them, we can take up to have a life worth of damage before the "transition" loads and we can be free from the grips of the portal. Seems mostly like it is suffocation damage, but I will look for fall damage now too after reading about it here. Also, It is not doesnt seem to correlate with traveling from a tall portal to a short portal. We have a bunch of those combos that dont cause issue. I haven't found a correlation yet, but am looking too.
Glitches still persist in the hotfix 1.16.201