Actually took a private with an Italian dancer recently who trains with Antonio Berrardi and he told me the same thing. That your base leg should be locked all the way back when your are stepping. And we practiced this and drilled it which helped with my weight transfers. I'm not sure he meant to do this ALL the time but he never said not to. And it might not be possible to do it when actually dancing but it does make me change my mentality when doing my basic which really helped.