When you have an upgrade that takes a long time, let's say a week, and meanwhile you upgrade your palace, then the help bar is extended another unit, but is not shown to your clansmen.

Example:

Palace at level 12 - 16 clansmen can help you.

You start upgrading knowledge that will take a week.

Your clansmen fill the helpbar, so 16 out of 16.

Then your palace gets upgraded to 13, and you also get an extra unit in the helpbars.

So the knowledge now has 16 out of 17.

The clansmen do not see this new opportunity to help, it will always remain in 16/17 until completion.