I've built a simple Find dialog (see endResult.png).

When the user resizes the dialog by grabbing the right edge and dragging it,
the
text field resizes but a gap that is larger than what it should be is displayed
between the text field and the Find Next button (see resize.png).

In the form editor after I changed the text field to be horizontally resizable
(by clicking on the horizontal spring in the floating alignment controller) I
resized the overall dialog by grabbing the right edge and moving it to the left
until it snapped to the correct size (with an appropriate gap between the text
field and the Find Next button).

Interestingly, I can avoid this problem by making just one change during the
laying out of the components.  Notice that the "Match whole word only" checkbox
is aligned with the baseline of the text on the "Cancel" button.  If I instead
align the "Match whole word only" checkbox with the top of the Cancel button,
this problem does not occur: if the user resizes the dialog the correct gap is
shown between the text field and the Find Next button.