I agree on not creating a new issue for 4.2, especially as we haven't decided if we actually want to backport it.
My perception - might be wrong? - on how we usually do these things is that the issue is marked as resolved when pushed on the main branch (master, we can imply that includes 4.3 in this context).

Then eventually things might get backported, in which case they use the same issue number. Normally I'd reopen the issue just to change the fix versions field and then close it again.
I think that's pretty normal as often we want to be conservative about backporting things, but at some point issues which where not backported are considered solid and people ask for them in previous branches: creating issues in advance is impossible, creating new ones as needed is an option but I find it rather confusing if the patch is very similar.