Before revision:  Moreover, we prove NP-hardness of this version even in case the horizontal and vertical segments of each L-frame have the same length. Finally, we consider the version, where every L-frame intersects a vertical and a horizontal line , and show that this version is linear-time solvable.
After revision:  Moreover, we prove NP-hardness of this version even in case the L-frames intersect a vertical as well as a horizontal line , and show that this version is linear-time solvable.