My company is building an App Engine application. The app encounters a bug (possibly due to an issue with App Engine itself, as per our research) on IE9, but it cannot be reliably reproduced and is experienced by a small percentage of users.
The workaround is to force IE9 to use IE8 mode. As a lazy front end developer (who doesn't like CSS hacks, shims and polyfills) I think it's OK to at least try going back to IE9 mode and see what happens, while we're still in private beta. The senior engineer (being more pragmatic) would rather that we continue forcing IE9 users to use the older IE8 mode. Who is right?