I just did a test. I placed 2 S4-36 focused them to a focus point. I Drew beams - everything ok. I then duplicated them, moved them to the oposite side of my plot, rotated them, and then selected "draw beam" they worked fine.
I them went back and did the same thing but - grouped them, moved and rotated them, then ungrouped, and drew beams - they worked fine - so i don't understand why you are having problems.
1) what type of instruments - do you have the same problem with all types?
2) what version of SL?
3) what platform are you on?