Cards being to expensiv, possible bug?

i hade a strange thing (possibly bug?) happen to me when i played DH earlyer today. some cards seamed to cost 1 mana to much, even though there whas no effect in play that would increses their cost.
Skull of Guldan was 6, eye beam on outcast was 1 and impriaoned anatean was 6.

is this a known bug or somthing new?