This is going to be difficult to describe... I had tried to format the other QString constructors by hand like the first one by typing "::number" in the proper place, clicking immediately to the right of the variable within (these are all unsigneds), typing ", 16" and moving on to the next one. The crash was reproduced a few times this way, sometimes after the first change, sometimes the second or third. It must've had something to do with clicking in the next place I wanted to be with the mouse while the autocomplete menu was still open.

return QString::number( port, 16 ) % ',' % QString( device ) % ',' % QString( index ) % ',' % QString( id );