Hey guys this is a problem I have not been able to figure out for a long time, I had the same problem in UDK actually.
When I make something such as a window with panes or a widows with bars it will do one of 2 things: cast an incorrect shadow (For instanced the bared window is casting as an octagon rather then a square window with bar shadows) or shine in light with no shadows (The room will be dark thus blocking outside shadows but on smaller pieces of BSP, bars, panes, etc will not show up.)
I have the the light-map resolution of my BSP set to 4 and directional light stationary with light mass set to 50. I have tried setting the mobility to static, mobile, and stationary. I have played around with everything from shadow exponents to cascaded shadow maps. After 5 and a half straight hours of researching and experimenting I decided to ask haha.
You might want to post an image so that others can better identify the problem.
Usually problems with the shape of stationary shadows are caused by the lightmap resolution, although 4 should be more then fine unless you are working at a very small scale. Also, what exactly do you mean with lightmass set to 50? There are multiple values for lightmass you can tweak, but they mostly influence indirect light not the shadow shape, with the exception of a static light’s penumbra.
With such a small window and a very dark floor I wouldn’t expect much light to get in, but still you would expect to see something. (Unless the base color of your floor is black)
What did you do differently when you got the incorrectly shaped shadow? As that one should be easily solvable.
Do you see any light on the floor in lighting only mode?