Ok, got it fixed:

http://git.savannah.gnu.org/cgit/screen.git/commit/?id=8ffd5f465ef4ed07b45534393ed51502b9b0ea77

will be in next bugfix release

Sorry, below was the fixed hardstatus line.  The broken one (with the %=) is:
hardstatus string '%{= kG}[ %{G}%H %{g}][%= %{= kw}%?%-Lw%?%{r}(%{W}%n*%f%t%?(%u)%?%{r})%{w}%?%+Lw%?%?%= %{g}][%{B} %m-\
%d %{W}%c %{g}]'

I'm currently using the following caption line:

caption string '%{= kG}[ %{G}%H%{g} ][ %= %{= kw}%?%-Lw%?%{r}(%{W}%n*%f%t%?(%u)%?%{r})%{w}%?%+Lw%?%= %{g}][ %{Y}%l%{g} ][ %{B}%m/%d %{W}%C%a%{g} ]'
caption always

On 066b098a312e5c from git, on Snow Leopard in Terminal.app this produces some odd results as shown here.

When I select one of the middle windows, everything is fine (see screenshot middleselected.png), but when I select the last window the highlighting is incorrect (lastselected.png). Note now the "h" is red and the parens around the highlighted window are not.

The built in version of screen (Screen version 4.01.00devel (GNU) 2-May-06) does not exhibit this behavior.

If I remove the first '%= ' to left justify the window list, the coloring works as expected.

My screen was compiled using:

 ./autogen.sh
./configure --enable-locale --enable-telnet --enable-colors256 --enable-rxvt_osc --prefix=/usr/local
make install

gcc version reports as i686-apple-darwin10-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5664)

Let me know if you need any more information. Thanks!