4 regular skill + 1 ult bug

There is a bug that sometimes lets you take 4 regular skills and 1 ultimate instead of 3 reg + 2 ult. But when you select your hero one of the regular skills is missing so you are left without 1 ultimate.

I have attached screenshot, it happened with this combo, but i've seen it happen with other skills. I don't know what specifically allowes it, as if you have selected 3 skills it normally says you cannot select more.