Found a lil' bit here: http://rtfm.modx.com/display/revolution20/Upgrading+to+2.2.x#Upgradingto2.2.x-StaticElements

One irritating little "gotcha" I ran into while using this feature in my MODXpo workshop was when converting an existing element into a static element; for example converting the existing default template to use an HTML file from a downloaded free template. I was converting it to static, deleting the existing content, then saving. Thus saving the empty content to the file! So it's very important to keep in mind that the feature works both ways... what you save in the Manager gets written to the file. If you have the template open in the Manager, changing the file via FTP won't automatically change what's in the Manager's content field, and you need to refresh the Manager page to get the new file contents.
Agree, that is something i run into every so often.
MODX should really warn you if you try to save an empty static element when the file is not empty.
It is logical, it's just that at some points our thinking isn't precisely logical. Computers (unlike teenaged children) do exactly what we tell them to do; the trick is to understand just what we did tell it to do!