Role "Workplace user": users can't edit XML resources? [SOLVED]

On our hard way of upgrading 15 portal sites from OpenCms 6 to 7, we are still advancing - but here's another strange one (maybe someone can give us a hint):

We'd like to create a user type that just works as an editor login for adding, editing and deleting xml resources (plain html, xml-content etc.) within a certain site. The only user role we could find suitable is "workplace user". But it doesn't seem to do the job, we get the following error when trying to edit a resource, e.g. "/main/editorial/index.html":

Error reading resource from path "/main/editorial/~index.html".
Reason: Failed to read deleted resource "/main/editorial/~index.html", because it is not allowed to read deleted resources.

So the workplace user is not able to edit text resources? Furthermore, we could not find any other suitable user role. Next higher seems to be project manager, but he could manage projects in the admin view as well. This is not what we want, we just need a plain and simple editor user role.

Is there any way to achieve this? Or is the lowest usable user rank for editing always project manager?

Thank you in advance,
Roman