It seems that some warning inside scratchbox appears as error inside our autobuilder (this explain why the packages builds in your box and not into autobuilder)
So it's no exactly a bug to be fixed..

I have fighted a lot with that trouble while packaging fltk:
https://garage.maemo.org/builder/fre...log.FAILED.txt
and solved here:
https://garage.maemo.org/builder/fre...1.3.2-1maemo5/

Returning to your package, it seems it's missing "dh_makeshlibs" and i think you should upload it without /debian/*.shlibs.

Feel free to take a look to the latest fltk build to check if there is something that can help.