I use the standard ADW Launcher that ships with CyanogenMod 7 and have noticed a problem with the dockbar. NOTE this is the "hidden dockbar" you can reveal with a swipe, not the normal Android dock (LAB/RAB).
There is enough space for 6 icons on my dockbar but I can only add 4 before they start flowing off-screen to the right. In other words positions 1 through 4 have icons but positions 5 and 6 can't be used (first screenshot). Dragging a new icon onto them places it at position 7, which can only be revealed by scrolling the dockbar sideways (second screenshot). It's as if ADW thinks there are icons at 5 and 6 already but there aren't.
I have tried using Reset ADW in the settings but while it reset many ADW features it did not reset the dockbar, or solve the problem.
There was a time when only position 5 was locked as blank and position 6 held an icon, but in dragging icons around to try an get one to go into position 5, position 6also became locked as blank.