Added an example to demonstrate the bug. When you run rubber with -vv on a.tex then you'll see that the dependency b.tex is not picked up (and consequently a.pdf is not rebuild if it exists but b.tex is newer).
Interestingly the error disappears when you \usepackage{style/myinput} in a.tex instead of only doing it in style/bla.sty.
Added an example to demonstrate the bug. When you run rubber with -vv on a.tex then you'll see that the dependency b.tex is not picked up (and consequently a.pdf is not rebuild if it exists but b.tex is newer). style/myinput} in a.tex instead of only doing it in style/bla.sty.
Interestingly the error disappears when you \usepackage{