To the best of my knowledge, there is no difference in meaning between learnt and the single-syllable form of learned. This is supported by the answers to When do you use "learnt" and when "learned"?
I'm watching a TV show now, and one subtitle reads:
You learned their craft and you learnt it well.
I have absolutely no idea what could be the reason for the two different spellings here. It doesn't appear to be because of differences in pronunciation: I can hear a slight difference, but a later subtitle gets the learned spelling again even though the same speaker more clearly uses a t sound there.
Is there some logic behind this?