Titanium is a metal that does have it's own problems according to books on the SR-71 developement. Over ageing causes brittleness and a sample will shatter when dropped from desk height. The metal is incompatable with cadmium, chlorine or flourine. A line drawn on it with a Pentel pen will eat a hole through the metal in 12 hours. As hinted at in graham2400's post on the production line they had problems with bolt heads coming off which was caused by cadmium deposits left on the bolt heads by cadmium plated spanners. Got rid of the cadmium plated spanners and all fixed. As graham and Towerman suggest, perhaps an old lesson beind relearnt, or interreaction with the composite.