Since 9.1.5, when opening a merchant with the TSM addon window selected, a second ElvUI skinned, fully functional merchant window will appear in the upper right corner of the screen. If I press the TSM button on either window to disable the TSM Merchant UI, the ElvUI Merchant window will reset to the default location on the left side of the screen. Press the button again and the TSM window reappears the the ElvUI window moves back into the upper right corner of the screen, right on the edge.

I tested this with all addons disabled except TSM and ElvUI+S&L. And it happens with S&L but not without.

Will be posting this issue on the TSM Discord as well since I don't know which addon is causing the issue.

OK, just noticed:

I play Horde on one server, Alliance on another. I'm having this issue on my Horde server, but not on my Alliance server. Anything I can do to narrow down what's causing this?

EDIT: OK, I take that back. Just saw it happen on one of my Alliance characters.