It happened the same to me:

This seems to happen as well whenever the field Spelling variant of the Lemma is present on the page with a value. So once you hit back:

• you can reproduce the effect again just by reloading that page.
• The effect is not present if you clear the value inside Spelling variant of the Lemma and reload.
• The effect appears again if you enter again some value in Spelling variant of the Lemma, focus outside of it and reload agian.

Ah this is low-prio already 👍

do we know how many editors hit the back button when they are creating multiple lexemes, which is a use-case that we probably need to design a better solution for?

The fix might turn out to be a simple one, but investigating it might take time that we can put into figuring out what would a solution for creating multiple entities (items/properties/lexemes) in series might look like?