Is 一 not omitted in Mandarin when it comes to measurement classifiers followed by '半'? The other day I went to a Chinese supermarket in Toronto to buy one and a half pound of minced meat. I told the meat department operator that I want "磅半碎肉" in Cantonese. That guy gave me half a pound instead. I repeated my request in English, but he didn't seem to understand it. Then I said "磅半" in Mandarin. He still thought I was asking for 'half a pound' instead of 'one and a half pound'. 

Until a Mandarin speaking lady beside me said to him: "他想要一磅半的碎肉", then he gave me the correct amount of minced meat. 

I am wondering, in Cantonese, omitting the counting word '一' before a measurement classifier followed by '半' is a common practice. We usually say "寸半, 尺半, 磅半, 噸半" instead of "一寸半, 一尺半, 一磅半, 一噸半"

My question : 'Is 一 not omitted in Mandarin when it comes to measurement classifiers followed by '半'?

(I don't think I pronounced my order so badly that he didn't know what I wanted, because he did give me half a pound of minced meat at first)
No. It is not omitted.

In Mandarin, "一寸半, 一尺半, 一磅半, 一噸半" cannot be said as "寸半, 尺半, 磅半, 噸半".