Database model insert always returns 0

Although CI has a lot of documentation, I find it's not particularly detailed... which means looking at the system code to work out what's happening under the bonnet when one wants to do anything more involved than the basic examples in the documentation.

Of course, as this is "undocumented" usage, it is possible that the functionality one deduced (and has used in one's code) may change in the future... perhaps more of an issue in the initial releases of CI 4, but hopefully becoming less likely now that its matured a bit (?).