I have seen screws loosen up on a number of engines, several of them the OS carb screws. It doesn't happen very often but it happens. Ken pointed out the need to check and tighten screws after break end and maidens, it's a pretty normal thing to do. About 10 years ago I found the two carb screws for the OS two strokes hanging on a LHS wall and bought the pack, 10 years later I gave them to a friend after both his fell out of an OS .55AX. He never tightened anything after break in and his engine was so cowled you couldn't check anything anyway.
For myself, I haven't ever lost one. I run in the engine then just tighten the screws up while the engine is still warm. I never use any locking compounds because I have had problems in the past removing screws when needed. I don't check for loose screws often but every once in a while when I think of it I go through them.
New engines expand when they warm up and the screws loosen when the engine cools off. It's an operators problem if these screws loosen up, not the manufacture. I will be breaking in a new engine this week, after it is run a time or two I will tighten every screw on the engine. It's a must!!
In this case it will be an SK engine but the make doesn't mater at all.