Hi George,
The 1.4.x branch is still undergoing bug fixes. We expect the branch to be marked stable in 1-2 more releases.
I highly recommend trying 1.4.x if you are able to try it out on a test server. If you are still having issues with the rewrite rules, let us know how to reproduce the issue and we will be able to get it patched that much faster.
Regarding IE 11, I just tested it on my desktop and had no issues. However, when I tried accessing the web admin from my phone (using chrome), I ran into some issues, so I think the issues are related to how mobile browsers connect to the web admin rather than a specific issue with Internet Explorer.
Thanks for letting us know about this issue, we'll take a look at it.
Kevin