Sizeable forms don't scale when small fonts are used


I've made an application in large-font mode. When I switch to small fonts,
all non-sizable forms scale properly, including the controls on it. Except
for the sizable forms, these have the same size as in small-font mode
(should be smaller). The controls however are scaled properly.

What can I do to scale the size of the form itself the right way. The form
should stay sizable.