Can't do a "delta build" these days?

[Daniel Kasak]

Hi all.

I used to be able to run a build of a large project, which would only
build things I'd changed, and optionally things where there are new
git commits. I could disable the build of libs with new git commits
with the --disable-updates switch.

Some time recently, I started getting the error:
 App dir 'appdir' is not empty. Please delete the existing contents or
use --force-clean.

I was under the impression that my 'appdir' never used to get cleared
out. The --force-clean option removes all my downloaded tarballs, git
repos, and built packages. So I can still build ... but I now have to
build the entire project each time, which takes *ages*.

Has something changed?

Dan