I have seen that effect before, but with windowblinds. In the end it was not a setting with Litestep but with windowblinds itself.
I could not correct the effect with the windowblinds config. I ended up using builderblinds (now called skinstudio I think) to fix the problem.
There was a global value that kept borders that were wider (or thicker) than the standard windows borders, from being cropped off when windows were maximized. I could never figure out an exact pattern why it affected some windblinds and not others, but it was in that config where I fixed it for sure.
Seeing as styleXP has a reputation as being somewhat of a windowblinds ripoff, maybe its a related problem.