Essentially...yes this is expected functionality of SubmitForm.
Easiest way, in my opnion, is to use patch. So, on the submit button "OnPress" something along the lines of:
Patch(
<SharePoint List>,
Defaults(SharePoint List),
Form.Updates
);
ReestForm(Form);
This should submit the data to the SharePoint list all the same, and then reset the form to handle a new entry, always keeping it as FormMode.New.
If that doesn't work, you can use variables to set the form mode, which I can walk you through as well if you'd like.
Hope that helps!