Removing column only removes the header label and content, but not the column itself

Steps to reproduce:

1. Create new project
2. Right-click in hierarchy header, just above the scene name, and add any column, like Tag
3. Right-click the header again, and remove Tag

Actual result: Column that was used by Tag persists, only the column header label and its content are removed

Expected result: Column used by Tag is fully removed

Reproduced with: 6000.6.0a2, 6000.5.0b2