Not a big but very annoying issue.
I have Taskbar vertically on the left. Works well, I like it as it is. On two of my rigs I also have a tablet input device, which puts its own toolbar on Taskbar.
When Taskbar is not locked, the size of the icon is as it should be, the smallest possible as I've set it. When I lock the Taskbar, it seems the size of the toolbar icon is "randomized"; it can stay small as I want to, or it can be huge.
When rebooting, it's normally never the same size it was before shutting Windows down. It really is totally random.
Taskbar not locked: