Well as long as you make consistent mistakes, no problems
And now re-reading the info about the tools, the by-effects were indeed neatly mentioned, so I am solely to be blamed for having missed them.
I do however have one question: one of my style settings recently failed and I could not find the problem right away as even check book did found everything ok. Finally it turned out that somewhere in the text I had typed <P> (in capital), while the stylesheet setting was <p> (lowercase). My trusty T1 ignored therefore the setting with a funny result. These kind of errors can make you mad before finding them.
Is it possible that check book signals that there is a capitalization mismatch between stylesheet and text?