This is from 'Mothers and Sons' by Colm Toibin.
Nancy(mother) tells her two daughters and her son, Gerard that they are moving to Dublin.
The girls made jokes about the move, and asked further questions over the weeks that followed. They found out about schools and even wrote to one girls' school and received a brochure in the post. Gerard did not mention it, and grew grimly silent if the subject were raised in his presence. Nancy realized that he had told no one because he had no one to tell as he was no longer very friendly with any of his schoolmates and he was not close enough to any of the businessmen in the town to whom he looked up so much.
I could have just read it without much thought, but this somehow got my attention.
The Italic sentence is not hypothetical (unreal conditional). It is past real conditional.
I understood the sentence as 'Gerard did not mention it, and grew grimly silent when the subject was raised in his presence.'
So my logic is that 'the subject' being singular, 'was' should be used instead of 'were.'
What do you think?