I am having a same problem on Linux, Mathematica 10.0.01. My "solution" (if you are looking for it?) for dashing of the frame was to specify each frame part individually:
b = Plot[{x, x^2}, {x, 0, 10}, Frame -> True,
FrameStyle -> {{Dashing[1], Dashing[1]}, {Dashing[1], Dashing[1]}}, PlotTheme -> "Monochrome""Monochrome"]
Very annoyingly, if I try to do the same trick to fill plot lines, one of them gets "cut"
b = Plot[{x, x^2}, {x, 0, 10}, Frame -> True,
FrameStyle -> {{Dashing[1], Dashing[1]}, {Dashing[1], Dashing[1]}},
PlotStyle -> {Dashing[1], Dashing[1]}, PlotTheme -> "Monochrome"]