Perhsps testosterone is overwhelming the androgen receptors so that the small amount of DHT remaining after finasteride is binding with androgen receptors even less. So finasteride is reducing your DHT and then testosterone is beating it to the AR reactive sites.
When I was researching my first cycle I remember reading a post on a forum that test can effect your hair in both ways, for the better or for the worse. He claimed he saw friends hair flourish on the test and other friends lose it all. I didn't think much of it given its purely anecdotal, but just thought I'd share.
Ive cycled deca and my hair..to me..looked like it began to fill in quite a bit. Unfortunately a got deca dick for about 3 months. I didn't cycle with test which I should have done. But anyway that's awsome.