dragging dropping

Hi, indeed, you can't drag to a tab.

First solution: untab the images, or show them side by side with the Window>arrange>tile options.

(you can also configure the preferences>workspace to untabtab the images, and have them floating)

You can also try to right-click on the layer name, select Duplicate... and target the destination image.

A third solution, until a fix is out, is to CTRL+A, CTRL+C to copy the layer, Ctrl+Tab to select the other image, Ctrl+V.

That should work. I do it all the time. Try resetting your preferences. Go to (Mac) Photoshop>Preferences>General or (PC) Edit>Preferences>General. In the General tab click on the "Reset Preferences on Quit" button. Quit and then restart Photoshop. 

If you mean in a consolidated image window its been reported to Adobe and in this user forum. I expect Adobe will rectify the document switching problem that prevent  dropping the image on the other document.