Why does an SWT Composite sometimes require a call to resize() to layout correctly?

Sometimes we encounter an SWT composite that absolutely refuses to lay itself out correctly. Often we encounter this when we have called dispose on a composite, and then replaced it with another; although it does not seem to be strictly limited to this case.

When we run into this problem, about 50 % of the time, we can call pack() and layout() on the offending composite, and all will be well. About 50 % of the time, though, we have to do this:

Point p = c.getSize();
c.setSize(p.x+1, p.y+1);
c.setSize(p);

We've had this happen with just about every combination of layout managers and such.

I wish I had a nice, simple, reproducible case, but I don't. I'm hoping that someone will recognize this problem and say: "Well, duh, you're missing xyz...."