GenericSetup adds all import steps ever run to it's base profile, no matter where they are coming from (install, uninstall, ...). And it doesn't forget by default.
I came across this because on one site we have installed Products.Doormat. On uninstall, an import step is run, called "remove-doormat-content". Someone must have un- or re-installed Doormat some time ago on that site. Now when we want to install some other add-on, this import step is run as well, removing our existing doormat content. There is already a fix for this, but it's not yet released.
So how do we get rid of this import step? Looking at the GenericSetup code i found this method:
manage_deleteImportSteps which takes a list of import step ids to remove.
To e.g. get rid of the Doormat import step, open that page in your browser: