(1) is incorrect. Sparsebundles are capable of over-provisioning the storage below them _by design_. They always have been. They are, I believe, APFS snapshots essentially now. This behavior is consistent with most other filesystems with similar constructs.
> Sparsebundles are capable of over-provisioning the storage below them _by design_.
According to TFA, HFS+ sparsebundles reflect the limitations of their underlying volume, while APFS sparsebundles do not. Seems clear to me that this is a bug.
Sparse bundle disk images [1] are a more efficient way to store disk images on an underlying file system. They are a completely separate concept from the file system in the disk image itself (besides HFS+ apparently doing some intelligent free space reporting) and are definitely not implemented as APFS snapshots.
(2) is the real issue here.