Misunderstanding Double Heavy?

In the Chen Style Taijiquan Practical Method book, HJS writes the following in regards to Double Heavy:
When the left hand is solid the left foot must be empty. When the right hand is solid, the right foot must be empty. ... These examples show that if the hand is solid then the foot must be empty [or the other way around]. If the front hand and foot are both solid, then the front foot cannot move freely. -- Chen Style Taijiquan Practical Method by Hong Junsheng, page 24.
I basically understand this to mean that both the right hand an right foot cannot be solid, as opposed to the conventional understanding of double-weighted in that both feet cannot have equal weighting on them. However, how does this apply to moves like lazy tie coat in chen style? In this move, I believe both the right leg and right hand are solid, but if the above quote is correct, this would have to mean that perhaps while the right leg is solid, then the right hand is empty? This would make the left hand, the one at either the dantien position or waist position be solid? What then about single whip? In this movement, generally both the left leg and the left arm are solid, unless this idea attributes to the right hook hand being solid instead? This idea reminds me of something my first taiji taught me. He said that when doing brush knee twist step in yang style, even though the right hand is striking, we should focus on the left hand, the brushing hand. Likewise, in repulse monkey, don't focus on the pushing hand, but focus on the retreating hand. I believe his reasoning for saying so was so that we could stay centered and not follow the "yang" aspect hand. However, in both of those examples, it seems to contradict the notion of double heavy??? I don't know.. I think I'm missing something here. Any thoughts? [edited on 8/5/06 to include some extra information in the blockquote to improve clarity] [tags]HongJunSheng,chen,principles,emptiness[/tags]