Being broken (i.e. having an unfulfilled dependency, pre-dependency, or
conflict) is a property of the package itself and should not depend on
the package manager. The package manager, on the other hand, can help
you to resolve breakages that occur, for example, during an upgrade.
The thing to keep in mind with aptitude is that it will list packages as
broken if the currently scheduled actions would leave them in a broken
state; this does not mean that they are already broken at the moment.
I think the following happened in your case: You made aptitude believe
(maybe inadvertently) that you wanted to upgrade or newly install
certain packages. This would have broken some packages so aptitude
pointed this out and probably offered several options to resolve the
resulting problems (e.g. by removing packages which conflict with the
new packages/versions). You then canceled all operations by running
"aptitude keep-all" (or its equivalent from the interactive menu) and
your system remained in the consistent (non-broken) state that it had
been in all the time.
If you want to see again what aptitude wants to do to your computer you
can try "aptitude upgrade", "aptitude dist-upgrade" or "U" + "g" in
interactive mode. (Remember: "aptitude keep-all" is your friend when
things get scary.)
To find out if you currently have any broken packages on your system you
can run
aptitude search '~b'