GIMP :: Eyedropper Tool In For Instance Color To Alpha Dialogue

I'm on MacOS 10.9 (Mavericks). Using GIMP 2.8.8 (lisanet edition).

GIMP has been installed for many years on my computers, but first since it runs natively (without x11 or xQuartz) have I finally and entirely switched to GIMP for my raster graphic work.

I really like GIMP and I'm working on expanding my knowledge and respect this excellent programme very much. There are of course a couple of oddities when you are used to Photoshop (until 3 months ago). I'm getting there. Though one issue sticks out:

The use of the eyedropper tool for example in the Color to Alpha Dialogue. First of all I'm aware about the difference between the Color Picker (set colour from image pixels) in the toolbox and the eyedropper. I'm writing here about the latter. It simply doesn't work at all. When I open Color to Alpha... and then click on the color field (by default it's white #ffffff) the Color to Alpha Color Picker opens. When I select here the Eyedropper tool (Click the eyedropper, then select a color anywhere on your screen to select that color.) the following scenario happens: the cursor doesn't indicate a particular function (stays as standard pointer) - when clicking anywhere on my screen both dialogues, Color to Alpha and Color to Alpha Color Picker disappear (respectively they slip behind the main GIMP interface). I can't select any color! And when I manage to get the two dialogue windows back into focus, I have to wait a certain amount of time before any pressing of OK or Cancel shows any response.

Sometimes a random color gets selected but this is beyond my influence.

I guess it's a weak spot of the new native GIMP without any X11 wrapping. The windows managements has several weaknesses (i.e. GIMP/Hide). I also thought that it might be caused by the Single-Window Mode. But even without that the problem remains. All in all it's a very important function and without it the workflow involved gets very tiresome.