Try this:
Have the same -delete glitch. But I just found a pattern, which solves the problem for me. (Windows7 x64 Rhino 4)
Click - Show desktop button on taskbar (Rhino and Grasshopper window minimizes)
Click one more time - Show desktop button (Rhino window restores, but Grasshopper window is not)
Just double click Grasshopper window to maximize it, and the problem disappears.
https://www.grasshopper3d.com/xn/detail/2985220:Comment:604100