Please try the following version, and let me know whether it works:
https://www.dropbox.com/s/j4c55cgk0m7nvph/7tt_setup_beta_v4.5.7.1.exe?dl=0
Thanks.

Should be fixed in v4.5.7.

v4.5.7: Added a new advanced option, show_desktop_on_hover, which makes the taskbar to show desktop when a file is dragged over it (similar to Windows XP).

Done in v4.5.7: If the file "7+ Taskbar Tweaker.ico" exists, it's used as a tray icon.

It might help. It surely won't hurt, so please grab it.
Also, could you try running the latest beta version and see whether it makes any difference?

Should be fixed in v4.5.6.9 (beta).

The feature is available as an advanced option (show_desktop_on_hover) in v4.5.6.9 beta.