I just ran across something weird. It might be that I'm just not
reading through all the small print in all the 10.3 manuals, but this
just happened.

In an imaging directive bundle, there was a list of bundles that was
to be installed during imaging.
But after upgrading to 10.3, the imaging process suddenly was about 1
hour longer than before.
It turned out that one of the actions in the directive bundle was
disabled, and this action was to install a huge bundle.
So even though the action was disabled, it still ran through the
actions and distributed the disabled "install bundle" action.

I had to delete the action to prevent it from being distributed.
It might be working as designed, but here's a heads up to those with
the same problems.