Probably a bug in WordPress Importer

I’m working on a project that requires a large number of pages, no posts! Pages!
I was organizing pages using page parent feature. The maximum number of sub levels I achieved was 3. After that I exported all of those using WordPress export tool, thought it will be even more easier to import those back when need than to use classic mysql dumping and importing of the sql file.
The problem was that after import WordPress saved all my pages old sub levels placement (somehow, but not sure if that is 100% OK), but not correctly. This way a page that wasn’t owning child pages now has some of those.
A possible explanation of that is the fact that the ID’s of the pages were not followed one by one in a normally incremented way (some of the pages where deleted in time), and the ID’s count looked like this: 1,2,3,7,8,9,23,32,33… so on…
But, this was done before exporting the file, so the file shouldn’t be affected because of that. Anyway it happened!
Can somebody explain me this? Is this ok? I don’t think so….