That is because a square knot is a "binding knot", not a "bend". You need to use a bend to tie two ropes together. Many people misuse a square knot as a bend. With results as you stated ... the knot comes untied. Those who tie ropes together with square knots and then place their life in that knot's hands are often times Darwin Award winners. A square knot is a good knot, if used as intended - for binding things. It can be a terribly dangerous knot if used incorrectly - as a bend.

Now back to the subject of this thread. My StarFlash mirror is alive and well after maybe 7 (?) years in my survival kit. But after reading rafowell's very informative posts and links to signal mirror information, I'm wanting to go look for a glass one. I will probably buy/make some kind of hard case with padding inside to protect it. Maybe some kind of dual-use padding/fire tinder to wrap it in and then placed inside my Esbit stove.