They sometimes skip a page to match the next odd/even number.
For example, when a section ends in an odd number - page 5 - before an "odd page" section break, the even-number page in between - page 6 - is skipped altogether.
This creates a number of issues.
- It wreaks havoc with duplex printing for the obious reason. In a book-style printing, you want the odd-number pages to fall on the right side and even-number pages on the left. But skipped page will prevent this from happening.
- A page border applied to the first page of a section doesn't work, if the previous page is skipped. In the example above, you can't apply a page border to "first page of section"- i.e. page 7 -, if page 6 is skipped. The border will only appear if you add page 6. This is obviously a bug.