Sadly it is serious and in production code. (I left there 15 years ago, I suspect it isn't in production anymore)
Worse, it was a giant switch, and the target system didn't have enough memory for all the code so there were different builds and the user would select which to load.
There was code like
case foo:
doSomething();
#ifdef build_two
doSomethingElse();
break;
case bar:
SomeThing();
#endif
MoreThings();
break;
I’m not sure the author knew what was happening. It seems like it worked like this and they left it at that.
While this was the worst example he constantly wrote code like that. He could write code like that with few bugs faster than any other programmer I've ever worked with could write code. Management changed between loving and hating him, they knew what his code cost, but they also knew they were getting results fast when that mattered.