Using the workbench screen's TextAttr (by reference), then closing the
Workbench.

Modifying a gadget without removing it from the gadget list.

Relying on NewModifyProp() to do a full refresh, when you really
should have used RefreshGList().

Making icons whose imagery has only two planes of data but having more
than two 1-bits in PlanePick.  (one IFF-to-icon utility appears to do
this).  With deeper Workbenches, your icons will appear trashed.

Erroneously stuffing the ACTIVEWINDOW IDCMPFlags into the Window.Flags
field, where it's numerically equivalent to NW_EXTENDED.  This
instructs OpenWindow() to look for a tag-list that isn't there.
Symptoms are enforcer hits or delays during OpenWindow().  Outright
failure to open the window, or a crash seem possible, too.

