Thanks for the message. I did a bit more digging, and amended the definition. This version has a much more narrow focus than the other one does.

To give you some additional perspective, A appears to always be a problem or issue, and B shows a reaction to A that is different from the normal state of affairs.

To give an example adapted from a grammar dictionary I love,

受験のこととなると学生は急に真剣になる.

受験 is a "problem" in the sense that it is not a good thing. While students might not typically be very serious, they do (真剣になる) become so when it is exam time.

It's not that 完全マスター is wrong - it is a very good book for getting the basics of the grammar, and I've used it myself a lot in the past. But in order to keeps things from being overwhelming, it tends to leave out some of the finer points of the expressions.

If you feel comfortable with all Japanese explanations, this text is simply amazing: https://www.amazon.co.jp/%E6%97%A5%E6%9C%AC%E8%AA%...

Anyway, those two examples fall into the distinction I made before.

1) 酒好きだった父は、酒となると人が変わったように元気になった。

"When it comes to my father (who loves alcohol/to drink), when he drinks he gets so genki it is as if he's a different person."

This would not, as I understand it, work with のこと. As noted above, のこと is used for something that isn't considered normal or expected. People often change a lot when they drink, so something becoming overly energetic doing something they love (drink) can be considered normal.

2) 弟は、車のこととなると急に専門家みたいになる。

"For my younger brother, when it comes to cars, all of a sudden its like he is an expert."

Because of のこと, according to the above reference, this implies that the younger brother usually isn't an expert on anything so his expertise on cars is out of the ordinary.

That being said, on looking at this more carefully, this "out of the ordinary" situation can also be used when のこと is not present. So, it feels like while there are often times when they can be used interchangeably, there are also times when this construction (limited to nouns) can be used to show the distinction I initially wrote about.

Thanks for the reply - it forced me to look more closely at was being said and learned a bit myself!