What I expected to happen was...:
when trying to resize my minecraft window from small centered to vertical window by dragging it to the side of my screen so i could read a forum behind it. what i expected was that it would just move and resize the window.

What actually happened was...:
when the window resized the command in the command block disappeared and all the buttons(except the "cancel" button) greyed out. the text is actually gone, when you start typing again the text appears but the old command doesn't return. Also you can't save the newly written text in the command block as all the buttons(except the "cancel" button) remain greyed out.

Steps to Reproduce:
1. open a command block that has a command inside it.
2. once in the command block GUI use your mouse to drag the minecraft window to the side of your screen.
3. Keep dragging until the mouse reaches the edge of the screen and you'll see the outline of the window jump out to the center of the screen.
4. when the window resizes the text inside the command block disapears

P.S.
when you press the cancel button you exit out of the command block GUI and the command is back when you open it again.