Comment # 1 on bug 1181763 from Ignaz Forster

transactional-update not only prints a warning, the behavior is also documented
(see the third paragraph of the man page for example).

Changing the default behavior to assume `--continue` should not be done,
though: Not only would this be a behavioral change, it would also introduce the
risk that the user accidentally continues a testing snapshot vs. a known to be
working snapshot as it is now.
Sure this would make sense in certain use cases, but just appending the `-c`
option if desired shouldn't be that invasive, either.