Steps to reproduce

If inserted text is multilined it could shift selected pmenu item to another one:

In the asciicast you can see that after selecting the second item it inserts contents but selection is shifted to the first(previous) menu item.

Will try to come up with a simple reproducible steps later.

Context: I have added registers completion source for custom autocomplete to be able to complete the whole contents of registers in contrast to CTRL-X CTRL-R that completes only words from registers.

Expected behaviour

Selection in Pmenu should be retained

Version of Vim

9.1.1418

Environment

Debian12, bash

Logs and stack traces