Quote:

Why are you using particles?



There are plenty of reasons why he'd use particles over these functions. If it's a laser beam, or a smoke trail. If it's just a line, I agree, use those other functions.

As for your problem, wow, that is really strange. I can't see anything wrong with it. If no one else points anything out, I'd post something in the bug hunt forum (along with some screenshots of both alpha = 50 and alpha = 55).