But the "spec" uses that line, so you can't very well ignore it either. Most unixes also have this behaviour, so this isn't some nonconformant outlier, this is the standard behaviour. It might not be ideal, but most of the UNIX IO model and heritage isn't.

Apologies for assuming you didn't understand the behaviour when you said it "doesn't make sense": I'd assumed you meant that you were having trouble understanding the behaviour, rather than "all the application developers and unix implementors" that expect this behaviour, not understanding "the spec".