GtkLabel can shrink but not grow?

[Gus Koppel <gtk spamkiller bytechase cx>]

I have a problem with a GtkLabel with wordwrap turned on. It's on one
side of a GtkHPaned, so it's width is supposed to be adjustable by the
user at runtime. The GtkLabel is embedded in a GtkScrolledWindow +
GtkViewport to handle situations when the label becomes too narrow to
show all of its text. I expected the label to reformat its text
according to its width changing. That doesn't happen automatically.

Okay, then I connected a handler for size_allocate-events of the label's
parent GtkViewport. (I couldn't find another suitable signal.) Handler
gets invoked properly and I am able to determine the changing widths via
viewport_widget->allocation.width. Then I adjust the width of the
GtkLabel via gtk_widget_set_size_request (). The label seems to change
its width then indeed.

The problem: when the Gtklabel gets narrower its text gets properly
reformatted. However, when the label gets wider the text stays narrowly
wrapped, it doesn't expand again. So basically I am able to shrink a
GtkLabel but not expand it again. What can I do to achieve the latter?

I've been looking for a function to explicitly enforce recalculation of
wordwrapping but the only candidates I found seem to be static functions
in GtkLabel.c. What can I do to make the wordwrapping text of a grown
label occupy its entire area?