How Srila Prabhupada interprets it is that Vishnu's Yogamaya does not have the power to stand in front of Vishnu so she stands behind him. Here is what he says in this section of the Srimad Bhagavatam:
The invincibly powerful deluding energy of the Personality of God, or the third energy, representing nescience, can bewilder the entire world of animation, but still she is not strong enough to be able to stand in front of the Supreme Lord. Nescience is behind the Personality of Godhead, where she is powerful enough to mislead the living beings, and the primary symptom of bewildered persons is that they talk nonsense.
I think what he's saying is that Yogamaya only has the power to delude Jivas, not Sriman Narayana.
In any case, this notion of Yogamaya being embarrassed before Sriman Narayana is verses 59-61 of Ishwara Krishna's Samkhya Karika, which talk about Prakriti being embarrassed before one who has attained Jnana:
As a dancer desists from dancing after showing herself to the audience, so the Nature desists after showing itself to the Spirit. Generous Nature, endowed with the Attributes, without any benefit to itself, causes by manifold means the benefit of the Spirit which is devoid of the Attributes and which confers no benefit in return. Nothing in my opinion is more modest than Nature, who because (of thinking that) “I have been seen”, never again exposes itself to the view of the Spirit.
The only difference is that this is just a metaphor, because the Samkhya school saw Prakriti as an unconscious entity as I discuss here.
