I will check if with latest Asus firmware the same problem happen. If not,
can you check the differences between yours and theirs regarding Time Machine? I can test every test you build to help you reach this problem.
Please let me know. The only change that was made related to Time Machine is how it was compiled, as Asus's method was very hackish (they were hardcoding changes in the configure script, which is a big no-no in a development environment). If it works with the stock firmware I'll play it safe and just revert back to Asus's hacked build files, just in case.