In software development there is a type of defect called a heisenbug. It is named after the physicist Werner Heisenberg, who stated that the more precisely a particle’s momentum is measured, the less precisely its position can be known, and vice-versa. Likewise, a heisenbug is one which disappears when you add code or try to debug it using external tools.
When I posted about the intermittent problem with the Glowbek, I had no idea whether it was a hardware or software defect. Turns out, it was somewhere in the middle.