Hovering over an ungrouped taskbar item without tooltip does not bring its window to front
I'm using smooth tasks fork and I like it very much. As I prefer my taskbar to be on the top of the screen, I disable the tooltips as it interferes with the applications menus. (ie tabs of maximized chrome browser). I also disable the application grouping as I don't need it, there's plenty of space in the taskbar and making drag&drop is simpler when you have a task item for each window in the taskbar.
In this mode, I found out that I can't drag & drop anything to a window which is in background. For example: 1) Launch Thunderbird 2) Make thunderbird window maximized 3) click new mail. 4) return to Thunderbird main window, the new email window is now in background and not visible 5) try to drag & drop (to attach) an existing mail to the new email window.
You will see that dragging the mail towards the taskbar item of the "new mail window" does not bring that window to the front. Accordingly, there's no way to do drag&drop operation in this scenario.
the workaround is to re-enable the tooltips. Then, when you hover over the taskbar item, the tooltip appears, and when you hover to the tooltip, the window of the new email comes front and now you can drop your attachment to this window. (But I do not want tooltips as mentioned above)