I agree with you there. The onion weed I know of has small white flowers on long stems and long slender blades - and I believe it is a member of the Oxalis family. I tried for quite a few years to get rid of it in my garden while I lived in Sydney, but no matter what I did, I was never totally successful - and that included using Glyphosate (round-up) diluted as per the instructions, and even used neat. No matter how much of it I killed, more would come up elsewhere.