133dde41bb changed how 'fake user' flag is handled with linked data.
Previous behavior was a bug/inconsistency, in that the 'directly linked'
tag would be 'over-set' and never cleared, forcing saving references to
a lot of unused linked data.
Note that ideally, 'Fake user' flag should be ignored, and the only way
to decide whether to keep or not a linked ID should be whether it's
actually used by some local data.
However, #103867 and #105687 show that this is causing issues in some cases,
where users wrongly relied on the linked data's pre-defined 'Fake user' flag
to keep their linked data in their production files, even if said data had no
real user.
While not ideal, for now we should consider 'fake user' flag for linked data
as a real usage case. A better handling of this edge-case is related to
wider designs aboud handling of 'non used' data on file save, whether
linked IDs should keep track of being explicitly or implicitly linked by
the user, etc.
Bastien Montagne
a60f651502