With the changes made to portal linking in 19w36a, it is now possible for portals in the Overworld to lead to existing portals above the Nether's ceiling (which is not possible in previous versions); I'm unsure whether this is intended behavior or not.

How to reproduce

1. Construct a nether portal in the overworld and enter it

2. Break the newly generated portal in the nether

3. Build another portal at the same location, but above y=128 (i.e. the nether ceiling)

4. This portal should lead to the original portal in the overworld (which is intended), AND the portal in the overworld will now lead to the portal above the bedrock ceiling.