Nope, it’s not a bug. If you want more information about it, you should check the official Dino Storm forum.
Anways, here’s the gist of it, it used to be pay large sum of 8Xk DD first then you can proceed to upgrading dinos. (besides coelo b/c coelo’s the beginner dino). But now, it’s like pay as you level.
Hope this helped. ^^