I just noticed this, and maybe it's a bug, but in case it's not... right now, when I sort by "progress" on my currently watching list, the progress is judged by the largest number of episodes seen regardless of a drama's length.
So, if I've seen 21 out of 41 episodes of one drama, and 7 out of 10 of another, the 21 episodes appear first instead of the 7 because of 21>7. BUT, the purpose of sorting by progress is how far you've gotten RELATIVE to the drama's length. I'm actually closer to finishing the second drama because I'm 70% through, thus my progress in it is bigger than the 50% of the other drama.
So, I think it would be a good idea to upgrade this feature so that "by progress" would be based on percentage completed of the show and not just 2 > 1.