Delete button not answering - solution

Solution found by Maxim Baraliuc :

Have the same -delete glitch. But I just found a pattern, which solves the problem for me. (Windows7 x64 Rhino 4)

1. Click - Show desktop button on taskbar (Rhino and Grasshopper window minimizes)

2. Click one more time - Show desktop button (Rhino window restores, but Grasshopper window is not)

3. Just double click Grasshopper window to maximize it, and the problem disappears.