Package changelog lists forked entries and parent Debian entries intermixed:
gnome-calls (0.3.2-1pureos1) byzantium; urgency=medium gnome-calls (0.3.2-1) experimental; urgency=medium gnome-calls (0.3.0-2pureos2) byzantium; urgency=medium gnome-calls (0.3.0-2pureos1) byzantium; urgency=medium gnome-calls (0.3.0-2) experimental; urgency=medium gnome-calls (0.3.0-1pureos1) byzantium; urgency=medium gnome-calls (0.3.0-1) experimental; urgency=medium gnome-calls (0.2.0-2pureos1) byzantium; urgency=medium calls (0.1.8.0pureos0.1) byzantium; urgency=medium gnome-calls (0.2.0-2) unstable; urgency=medium gnome-calls (0.2.0-1) unstable; urgency=medium gnome-calls (0.1.9-1) unstable; urgency=medium gnome-calls (0.1.8-1) unstable; urgency=medium gnome-calls (0.1.7-1) unstable; urgency=medium
Seems the PureOS fork maintenance was done using a 3-way merging strategy, which results in a package becoming progressivbely looser tied to its parent - i.e. forking off further over time.
Please keep packaging close to its parent, by rebasing changes on top of latest Debian package release.