Created attachment 7321 Patch to fix alignment label (tasklist) When we switch from horizontal to vertical (and come back to initial state) alignment are not kept (like GtkMisc with alignment property). Patch fixes this issue.
Olivier Duchateau referenced this bugreport in commit 617aa7c7b9056ede24607e3c95555653bfbeabc8 tasklist: Fix alignment of labels when orientation is changed (Bug #13864) https://git.xfce.org/xfce/xfce4-panel/commit?id=617aa7c7b9056ede24607e3c95555653bfbeabc8
Thanks, really nice work in tracking that one down. I had only recently noticed it myself. And sorry it took so long to review and push the patch. Must've slipped by...
Fixed.