This is generally not an issue, but there are a few odd ways that abilities can at least attempt to have a creature become attached to another creature. Just to be clear, that cannot happen. If an ability tries to, the ability will fail and nothing will become attached. If something that is attached to a creature (an aura or an equipment) does become a creature, then that newly animated creature will ‘fall off.’

Here’s an example of this how this situation can happen. The artifact creature Myr Welder has the ability to exile artifact cards that are in a graveyard. The Welder itself then gains any activated abilities of artifacts that are exiled by this activated ability. If a piece of equipment is exiled, then Myr Welder will gain an equip ability. And while this ability can be played, nothing will happen as the Welder is still a creature.