I've always updated Tumbleweed with
zypper dup --no-allow-vendor-change
(well, --no-allow-vendor-change is actually default now, but anyway). Until last time, it worked fine: it didn't try to change vendors. Or occasionally it proposed changing vendors for a few packages because of some dependency conflict; in those cases I had to confirm the vendor change as a conflict resolution (as it's not allowed to change vendors on its own authority).

Now I'm trying to upgrade, from 20181224-0 to 20190115-0, with the usual 'zypper dup --no-allow-vendor-change', and it wants to switch 248 packages from the official openSUSE vendor to all sorts of repositories I have added on my system: to Education, Games, KDE:Extra, packman, whatnot. It doesn't throw out any dependency conflict, just the final 'Continue?'. In fact it does the exact same thing as if I run 'zypper dup --allow-vendor-change'. Here is the zypper dup --no-allow-vendor-change output.

If I lock a package on which it wants to switch vendors, it doesn't give me a conflict either, so there is no dependency reason for it to switch vendors. In /etc/zypp/zypp.conf, solver.allowVendorChange is left commented out (with the default being false), but nothing changes even if I explicitly set it to false. I've also tried updating the zypper package in the hope that it's a bug that has since been fixed, to no avail.

Has this happened to anyone, or do you have any solution or idea what causes this behavior?