Interestingly, I have no problems using IE9 for my MODX development, whatsoever. It works perfectly and I have rounded corners, and everything. Here is my set-up:
- I have compatibility mode turned off by default. (this fixed issues with a lot of sites, a long time ago). I turn it on manually, if I have to.
- I am using Windows Vista with out of the box settings. I haven't tested this on Windows 7.
- I have my rendering size at default. If things are appearing too big, I just use Ctrl+Mouse Scroll, to make things smaller. As a practice, I scrolled up the size and this created a lot of the issues mentioned in this thread. So I scrolled it back down to a usable size.
- There is an artifact on some buttons, a small line going across the top, but I've seen this before and it doesn't bother me.
- I have no extensions installed in IE9. I find that these screw up my development.
- Quip will return an Internal Server Error, but it doesn't stop the add-on from working. I mostly use the Articles Container, anyway.
Further, my own site uses standard CSS3 and renders near perfectly in IE9. So, maybe the fix is to uninstall extensions (from IE9) and turn off compatibility mode by default? I'm not sure as I could not replicate the errors you were having.
With regard to the MODX Forums.... These are indeed unusable, and it is because of the source (missing /divs). I use Chrome for anything regarding email or forums, so I never noticed it before.
[ed. note: fuzzicallogic last edited this post 11 years, 8 months ago.]