Syndra W/Ult interaction working as intended?

In a game today, I had 1 ball on the field and 3 balls captured in my W, which I threw out. Thereafter I ulted immediately because I was caught out and needed to flash out of range. I expected a 7 ball ult, but instead, only the single ball that was previously out was used and the target didn't die as a result. I can only assume this is because the 3 remaining spheres from my W were still in the air, but this seems like a serious issue - I don't think there's any situation in which one would rather have the W complete than have an extra 3 spheres in the ult. Is this working as intended?