Okay, last night I decided to do a little searching to see what I could find about the expression "working like blacks" or "working like a black". As I said yesterday, I'd never heard the expression in the US so I wasn't sure what to make of it when I first heard it here.
What I found is that the phrase is not just an Irish one, but is also used in Britain - apparently arising out of the British experience in Africa. The use of the phrase by one of the contestants in the last Big Brother series caused some upset. It also appears in Madame Bovary, which means it was once probably common in France too. (Maybe still is?). It's also apparently fairly common in Latin America, in Spanish and Portuguese. Regardless, it's not considered a positive phrase, which means that the benign explanation I was given in the 80s was wrong.
I was wrong about the phrase.
I found two uses of it in the official Dáil debates records. Both by James Dillon of Fine Gael. First reference was from 1937 and the second was from 1959.