Try using the drawn after shading argument in the subtitle sexp.
1: Image to display
2: X position, from 0 to 100% (positive measures from the left; negative measures from the right)
3: Y position, from 0 to 100% (positive measures from the top; negative measures from the bottom)
4: Center horizontally? (if true, overrides argument #2)
5: Center vertically? (if true, overrides argument #3)
6: Image width, from 1 to 100% (0 uses original width)
7: Image height, from 1 to 100% (0 uses original height)
8: Time (in milliseconds) to be displayed, not including fade-in/fade-out
9: Fade time (in milliseconds) to be used for both fade-in and fade-out (optional)
>>>>10: Drawn after shading? (optional)<<<<
Setting it to true should make it appear over top any fadeouts.