Hi,
Normally the font size you choose in the Tools - Option - Editor Format dialog gets saved in the registry and therefore is a permanent setting. You can take a look (or even try it directly) at HKEY_CURRENT_USER\Software\Microsoft\VBA\7.1\Common\FontHeight.
There have been some reports for years that this permanent saving to the registry does not work. Most of them come from Excelians. Cause unknown. It is not clear if it is due to Office or VBA, Windows, a certain permission situation for the registry, some graphic setting/situation or whatever.
Servus
Karl