Steps to reproduce the issue

Create a new template in J4 with a module of same name as one in Cassiopeia, e.g. 'breadcrumbs'
Create two modules, one assigned to the 'breadcrumbs' position in Cassiopeia, one to the 'breadcrumbs' position in the new template.

Expected result

Only one of these modules should appear in either rendering.

Actual result

Both modules are displayed:

It happens whichever template is assigned as default.

System information (as much as possible)

Joomla 4 Beta 3 and also Joomla 4 Beta 4 nightly from 02/09/2020.

Additional comments

I appreciate that in the end it is unlikely that anyone would assign two modules of the same name and type to the same page, but for testing purposes, it's a bit confusing.