In Draw, the sidebar is immediately updated if Format - Page style changes the background. But in Writer, some external trigger (like print preview) is needed to cause that information to refresh. -changing the paper size forces a full refresh, but changing "Right and Left" to "Mirrored" doesn't. Steps to reproduce: 1.) start a new writer document and open the sidebar - look at page properties and see that background is set to none 2.) Format - Page Style and change the Area from None to a Color. Expected: the sidebar should be signalled when the background fill is changed. Actual: background still reported as NONE The "page" sidebar was developed during LO 5.3 as an experimental feature, and acted this way right from the beginning. But this looks like it is a missing invalidation issue in cui/source/tabpages/tpbitmap.cxx, not a sidebar issue.
The sidebar feature was added with commit d02f75a8c36705924ddd6a5921fe3012fafce812 Author: Oliver-Rainer Wittmann on Wed Apr 10 08:20:16 2013 +0000 Resolves: #i121420# merge sidebar feature where sw/source/core/doc/docdesc.cxx set out its current invalidations. Since background was added to the sidebar after that, I expect it just needs an extra invalidation when the page style is changed.
Fixed in master with https://gerrit.libreoffice.org/c/core/+/176300. This bug was fixed for the benefit of bug 125969.