Odd. I wonder what triggers this on your computer when we can't reproduce this anyone of us.
I can reproduce this, but it takes a very specific set of conditions.
First, the main jAlbum window needs to be shrunk down so that it is significantly shorter than the skin's settings panel. This is why no one else seems to have encountered this before - I suspect most users don't do this, and in most skins, the settings panel isn't huge (I make sure mine are smaller than the typical low-end laptop monitor - anything larger than that is almost aggressively unfriendly).
Second, you need to move the jAlbum window very close to the top edge of the monitor. You can't slide it hard against the top, because that just triggers Windows "maximize" behavior.
If you now open the skin settings, the top bar of the window will be inaccessible with the mouse.
There are two fixes for this. Simplest is to close the settings window (just click OK, or hit ALT-F4), drag the jAlbum window down and/or make it taller, and open the settings again. For a one-shot fix (i.e., Windows doesn't remember it), use the keyboard: ALT-Space, then M, then use the arrow keys to move the window down.
This doesn't occur in macOS. In macOS, no window can be positioned so that its top bar is invisible on the monitor. So, should jAlbum struggle to overcome a rare case that's actually just a Windows bug?