Putting a panel on the LEFT side of the screen, with the normal "Window Buttons" on it, the text on these Window Buttons is incorrectly oriented. They read as if their "up" is facing *towards the center* of the screen (i.e. to the right) instead of *away from the center*. To fix: Please make it so when the Window Buttons option "Rotate buttons in vertical panel" is checked, then the text's "up" is pointing to the left for left-hand panels, and right for right-hand panels. ... This is both a regression and counter-intuitive. Between Xfce 4.6 and 4.8, the Panel Properties *reduced* the ways to specify these particulars of the orientation. They used to have a box that let you select from all of 8 qualitatively different positions. And when the panel was on the left-side (vertical), the Windows Buttons had their "up" facing left, and correctly flipped when on the right. The window buttons orientation is broken in 4.8 for vertical panels on the left side of the screen. Most would put the vertical panel on the left, I would think, because scrollbars for windows are typically on the right.
There is another bug that has screen-captures as attachments from the setup I am talking about. See Bug 7656 attachment 3878 . They have a left-hand panel and you can see the window buttons are facing the wrong way. Hope this helps. (https://bugzilla.xfce.org/attachment.cgi?id=3878)
Created attachment 5231 screenshot showing the problem I added a screenshot. This is from xfce4-panel 4.10.1, so this is still a problem.
To be honest this is intended behavior. The text is rotated only in one direction vertically - not only in the window buttons but in all plugins. So it's consistent at least, even if it's not what you want.