as far as i understood things transition would not happen if a package that was patched by us would be overwritten by an unpatched version in the archive.

But when calculating updatetability it seems e.g. amber-security does not take amber-phone into account for that. So we currently have

libwebkit2gtk-4.0-37 2.26.2-1~deb10+1 in amber-security and 2.24.4+1327+git7613748bb-1pureos0 in amber-phone-staging so users get the upatched webkit.
While this doesn't break anything substantia atml if the same happened with e.g. gtk3 the phones would become mostly unusable.