Inserting Unicode thin space changes line height

Thanks to participants to this forum, I found yesterday a very efficient way to create a shortkey in order to insert thin spaces in a text I am writing with Pages.

As I am starting to do it, however, I am confronted with another issue, that is not related to the way I do it, but to the Unicode insertion itself.

Let's summarize the issue.

If I insert - through whatever way, for instance by using PopChar - a normal space, breakable (code 0020) or non breakable (code 00A0), everything goes fine and result is exactly what one could expect.

However, when I insert a thin space (code 2009), or another similar shorter space (code 2002, 2003, 2004, etc...), the line height changes, and it is optically noticeable: exactly as it used to happen with some older word processors when introducing an exponent, a wider space is introduced between the line where I insert the thin space and the line above, and one sees the line slightly changing position when it is done (like going down a little bit).

If I would need to insert only a few isolated thin spaces, it would not be a real issue. But since I need to insert many of them, it is a real problem.

Interestingly, the problem only occurs with the insertion of a special space size. And while it happens both with Pages and Word, it does not happen with Mellel.

Of course, I have made sure that PopChar is set to the same font as the one I am using in my text, and not to Lucida Grande - but to no avail.

This presents a serious problem. What can I do? Is there any way to solve that?

If you own both PopChar and Pages, or insert Unicode through any other way, you should be able to reproduce the problem. Try to insert a thin space (code 2009) in the middle of a multiline text, and you will see.

If I would have known earlier, I would have typed my text with Mellel - I had considered it, but didn't do it because I needed to insert pictures with legends below, and this can more easily be done with Pages. Too bad: now I have a 120 page long text I am revising, I need to insert thin spaces at many places around the text for typographical reasons (it is a text in French), and I am stuck with an irritating problem. It will still take me three days to revise my text, and after that I will insert the thin spaces through a few bulk changes where it is typographically required, but I am wondering if this will be possible without creating irregular line spacing, which would be ugly.

Any suggestion to solve the problem most welcome! A solution had been found to solve my first question yesterday, so I still feel hopeful for an answer to this one too!