Two product defects (#28094 and #28288) in 7.0 up to SP3 and 7.1 up to SP1 are responsible.
With #28288, development confirmed a bug where some relations for QBMClrType are incorrectly restricted as Delete Cascade.
With #28094, development confirmed a bug where superset handling of DPRShell relations incorrectly deletes DPRProjectionStartInfo entries.
The fixes for both defects will be included with 7.1 SP2. Due to the complexity of the fix, no hotfixes are available.