InfoPath Dev

When using InfoPath from (list) I found out a weird bug... I have a people picker field in the form. When creating a new item I can fill it by rules with an user (f.e. userName() or based on other list) However when leaving the field blank and edit existing item the rules to fill the user field doesn't work the people picker field keep blank. But when it is filled on creation then it is able to update by rules when I edit the existing item in the infopath form Anyone has a solution to this issue to fill the blank user field when edit existing item?

Yes, I've seen this before - that rules to set the people picker only work on new forms. Are your rules on form load? Or a button or another field?

I tried both: Button and On load. Strange thing: when it is initially filled it is able to update it in the edit form.