When using Drift + TSM, when I go to a vendor and open the TSM-style window, the default Blizz window stays opened as well.
This happens only while Drift is active. Somehow it forces the Default UI Window to be active alongside with the TSM one.

Example screenshot: https://prnt.sc/SOsavg0r-Ahf

Thanks for letting me know.

Fixed in Drift v2.2.7.