Nocturne bug

I just had a bug with nocturne. here is what happen and why i did what i did. I was heading to lane to gank Siver. she started to run i wasnt in ult range but i popped it to turn out the lights for their team i would be in ult range in a few seconds any way. she popped her ult and ran to fast for me to get in range in time so i flashed to get into my ults range before it was to late. popping my ult give me a few seconds to get in range before i launch over. so when i flash i crossed the thresh hold of my ult launching me. i did launch BUT i didnt make it to the target. something with the flash combo cut it in half. i jumped the distance of 2-3 flashes but it was half the distance to the target. this is a ult that ALWAYS sends you to your target.