I have upgraded to 4.10pre and noticed that the action buttons are always reset to button style, instead of session menu.
I can confirm this bug on fedora 17 with the 4.10pre version from the siderepo: Name : xfce4-session Arch : x86_64 Version : 4.9.2
Nick and I debugged a bit and this patch will most likely fix the issue. http://git.xfce.org/xfce/xfce4-panel/patch/?id=25d6c24ddffed2e894cebbf4262c5aa9bcf4aae6
Fixed with another bug, but added workaround too in 4d9f193.