Even though I used tree-view alot lately, its the first time that bug happens to me. I debugged the situation down to some lines which seem to have the wrong order. This clearly is a timing issue .. as soon as I added prinf into the related method, the bug disappeared.
Meh, I failed to properly refer the commits to the bug. Here all 3 related commits: master: https://git.xfce.org/xfce/thunar/commit/?h=xfce-4.14&id=61d51a95859d61c6e2563d043cfb12fa35ac7b81 branch 4.14: https://git.xfce.org/xfce/thunar/commit/?h=xfce-4.14&id=61d51a95859d61c6e2563d043cfb12fa35ac7b81 branch 4.12: https://git.xfce.org/xfce/thunar/commit/?h=xfce-4.12&id=95925eb023144ebe199234b65bafc1f08696f5de This as well seems to fix a delay when opening tree-view.