Hi Karl,
We're glad you found metaPost and we'll do all we can to make it work right for you. I think the issue you had with WLW overwriting changes you made while editing the content online may be a result of the fact that you still had the original instance of WLW open with your post. If this is the case, then WLW hasn't had a chance to update its content from the web and changes you make to this original content will overwrite any changes you made to the version on the web.
In most cases, this won't be an issue because people will have closed their post in WLW before coming back to edit it. If you haven't closed your post, then all you need to do to see the changes you've made from the web is use the Open menu to open the post.
While the cache setting for your module wasn't the cause of the overwriting you noticed, it will cause some issues when you edit content from Windows Live Writer. Logging in as admin or host will allow you to see your edits, but I realize that this isn't optimal, and of course, optimal is what we're shooting for.
I've taken your comments to heart and have changed the Text/HTML provider so that it automatically clears the module's cache for you when posting from WLW, regardless of the online cache setting. I'll be putting this up on Snowcovered after I've had a chance to do a little more regression testing. With this patch, you'll be able to leave your cache settings as is and still see your WLW edits. I've also updated the Text/HTML provider to take you directly to the page you've edited to help save some time.
Thanks for the awesome feedback Karl!
Don