Book (INDB) requires specific Save-As, every time?

I know there have been posts about this but I can't dredge any up.

When I close a Book (INDB), InDesign insists on treating it as modified/converted file and a new name or a confirmation to overwrite the existing one. Has this always been the behavior? Is there a point to it, or is it simply an overlooked glitch in file handling?

(v20.1/Win11, but I've encountered it since at least v19.x. Don't recall the last time I worked with a Book project, so can't say if it occurred in any prior/less recent versions.)