I had multiple JHS apps open in JDev and had multiple copies of the editor open. I closed some of the apps without closing the JHS editors. Now when I try to open the JHS editor it shows up on my Windows taskbar, but I can't actually get the window to show up on screen. I've tried closing all the apps in JDev and re-opening. I've tried re-starting JDev, re-booting the machine, and even re-installing JHS. I guess the next thing to try is re-installing JDev.
edit: same thing happens if I re-enable JHS on the application, or create a brand new app and enable JHS.