Copy Job: Using variable library prevents editing mappings

Sorry I have barked the wrong tree and thought that the problem was in Variable Library, but it is not. Problem is that Copy Job does not support files from subfolders. I can now reproduce the error consistently. 

Steps:
1. Create new lakehouse (with schemas)
2. Create subfolder under Files section and upload CSV file (lets say abc.csv) into subfolder
3. Create new Pipeline and add Copy Job activity
4. In Copy Job select CSV file from subfolder as source data
5. In destionation type in a schema name for example def and give any table name. I used def_table

6. Import schema and save the Copy Job. Everything seems to work now.
7. Next we need to edit the Copy Job. Open same Copy Job and click "Edit mapping".
8. Click Edit column mapping
9. Fabric seems to cache the column mapping, so it seems to work now. Click reset column mappings and then click import schemas. This reproduces the error.

This results the same error message as I have: Lakehouse operation failed for: Operation returned an invalid status code 'NotFound'. Workspace: 'd6dde882-24c5-4854-882a-7d44e6386811'. Path: '34148136-1ada-4da5-bb25-62a0a9b487f9/Tables/dbo/subfolder'. ErrorCode: 'PathNotFound'.

Notice that it tries to read data from Tables/dbo/subfolder, but it should read it from Files...