Why would it be "wrong"? It works doesn't it?
Functionally, having two tables linked in a one to one relationship is nearly (not quite) identical to putting all the fields from those two tables all in a single table. It's a trade off of having shorter field lists in your table schema vs. a more complex relationship map.
all the books and forums say it is a no-no, so I was just looking for anything I may have missed since it is working great.
Sorry, but in many years of database work, never saw any such warning stating that it was a bad idea and thus can't see any reason why it's "wrong" to have two tables in a one to one relationship.
From the Filemaker Missing Manual
"As a general rule, unless you can articulate a good reason for its existence, a one- to-one relationship is a mistake: It’s just two tables where one would suffice. (For some clarification, see the box below.) You’ll almost always want to combine entities like people and their addresses into one table."
"unless you can articulate a good reason" would seem the operative phrase there. In my opinion, that sentence overemphasizes the negative by calling it a "mistake".
Adding a second table linked in a one to one relationship complicates your relationship design so you don't want to do this unless you have a good reason. But you already indicated that this was working for you and your reason for making this design decision.