Simply the title. You can walk away from the end portal or nether portal and they will unlight, The nether portal isnt that big of a problem just keep a flint and steel but the end portal. You have to go into creative and break and replace the portal frame piece

They shouldn't and last time I checked, they didn't.
I'll be needing more info than that. Versions? Other mods? Etc. Maybe give this article a read.
Do you maybe have some other mods which may be killing or otherwise interfering with the portal entities?

0.2.5 Betters portals.
https://gyazo.com/33798e12ea46ab77efc9cdfcc81a699d
https://gyazo.com/c83195560a7f9c41d6b050e820eb8ff4
Aether II is the only other mod with a dimension to my knowing.
And in terms of bewitchment I have noticed with the end portals and flying brooms it bugs the brooms out. But that probably has nothing to do with your end since bewitchment is a beta mod.

It doesn't necessarily have to be a mod which adds dimensions. Try removing all third-party mods and see if that fixes it. If it does, try to find the minimal combination of mods which still cause the issue.
I'd still suggest reading the article I linked above.