In minecraft 1.8.1 and below press Alt+Tab while holding W, for example, would let you use your mouse for other things but the W input would still be present on minecraft meaning you could walk while sorting out other stuff.

This is not in any way a serious issue but it does mean I'll be sticking with 1.8.1 until I can no longer use it on my server (server is running 1.8.4 don't worry) as I enjoy multi-tasking when I play minecraft. It also makes some AFK farms harder to use.