MekHQ select Campaign Preset box behind splash (Linux specific)

We get reports of new campaigns in MekHQ and on Linux appearing to freeze, looking like this.

Often the cause is the "Select Campaign Preset box won't come forward

One of our Linux players was able to fix with this.

Using alt-space when the mouse pointer is around the center of the image, the pop-up window appears, and I click on "Move" instead of "Resize". Then, the pointer becomes a kind of a cross. Now I move the mouse (without clicking) out of the image and the type-of-campaign window appears from behind the image when the mouse pointer is outside of the image. Once the window is outside, you can whatever is needed.