In Brahma-samhita (5.54) it is said, karmani nirdahati kintu ca bhakti-bhajam: “For those engaged in devotional service, bhakti-bhajana, the results of past deeds are indemnified.” According to this, Bharata Maharaja could not be punished for his past misdeeds. The conclusion must be that Maharaja Bharata purposefully became over-addicted to the deer and neglected his spiritual advancement. To immediately rectify his mistake, for a short time he was awarded the body of a deer. This was just to increase his desire for mature devotional service. Although Bharata Maharaja was awarded the body of an animal, he did not forget what had previously happened due to his purposeful mistake. He was very anxious to get out of his deer body, and this indicates that his affection for devotional service was intensified, so much so that he was quickly to attain perfection in a brahmana body in the next life. It is with this conviction that we declare in our Back to Godhead magazine that devotees like the gosvamis living in Vrindavana who purposely commit some sinful activity are born in the bodies of dogs, monkeys and tortoises in that holy land. Thus they take on these lower life forms for a short while and after they give up those animal bodies, they are again promoted to the spiritual world. Such punishment is only for a short period, and it is not due to past karma. It may appear to be due to past karma, but it is offered to rectify the devotee and bring him to pure devotional service.
Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Fifth Canto, Chapter 08 – Text 26