I just hit level 80 in the battlepass without purchasing it. After hitting 80 I decided to buy it using Overwatch Coins. I had 1400 coins and it costs 1000. After the transaction all the Premium rewards unlocked however the 400 Premium currency in the battlepass was not added to my accound balance. I may not be a math wiz but 1400 - 1000 = 400. If you add in the unlocked currency i should be at 800. However, I am sitting at 579.
I really only wanted the Mythic prisms anyway, but i think I should still get the remaining currency I am due.