Currently, one needs to call reset_view after calling set_part to refresh the view, and show the next part of the document. Ideally, set_part should do it internally.
I'm setting this to NEW as no one will confirm this anyway..
Pranav Kant committed a patch related to this issue.
It has been pushed to "master":
tdf#97236: Refresh the view when part is changed
It will be available in 5.2.0.
The patch should be included in the daily builds available at
http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More
information about daily builds can be found at:
Affected users are encouraged to test the fix and report feedback.