de[endecy not build

Greetings,

I have a dep named libfoo which I handle based on a target file name libfoo.list.
in order to handle version bumps of libfoo I've defined the following dep tree:
libfoo depends on libfoo.list depends on libfoo-1.2.3.tar.xz

when I run the build flow, I see this in the log:
scons: building `output/libfoo.list' because it doesn't exist

and the build works ok.

when I update libfoo-1.2.3.tar.xz to libfoo-1.2.4.tar.xz and run the build, I see this:
deps/libfoo-1.2.4.tar.xz' is no longer a dependency
deps/libfoo-1.2.4.tar.xz' is a new dependency

I expect that output/libfoo.list will be rebuilt but it isn't. why is that?

Thanks,

Dagg.