Not sure what you're seeing there.
You can bid up to 10 days without needing the next week's slot open. If you bid more than 10days, then you need to be able to hold the next week's slot as well.
CBA 7.C.5. For vacation award purposes, a vacation period that extends into a subsequent vacation slot by 4 or more days shall occupy both slots.
You might be misinterpreting the leftover vacation days rule? You can't bid a vacation that leaves less than 7 days in your bank.
CBA 7.D. Splitting Vacations
A pilot may split his vacation into as many as 4 separate periods provided each period contains a minimum of 7 days vacation;