I just upgraded to WB 5 but I was having this problem with WB 4 as well. I have my taskbar at the top of my desktop, not at the usual spot on the bottom. Whenever I try to maximize any windows, they go right to the top of the screen; they don't maximize to the bottom edge of the taskbar. This happens no matter what theme/skin I am using in WB. Right now if I press maximize, the window will maximize to the top of the screen and cover the taskbar; on a previous reboot, when I pressed maximize, the window would maximize to the top of the screen, but underneath the taskbar so that I couldn't even see the titlebar of the window. This has nothing to do with my taskbar (set to be Always on Top as it has been for years).
I probably should also add that sometimes I will have an issue lasting for a few days where if I maximize a window, it goes so far off the screen that the titlebar and the menus of the window are up even above where the taskbar would be (e.g. I can't see them at all!)