It seems that at least those sticks I have, are not that bad.

I test­ed the first stick which failed first on Solaris 10u9 and the sec­ond stick with anoth­er FreeB­SD machine, and both do not show traces of prob­lems there. The first stick attached back to the machine which exhib­it­ed the prob­lems ini­tial­ly shows prob­lems again.

To deter­mine if it is the USB hard­ware or the FreeB­SD USB ker­nel sub­sys­tem, I will step by step update the oth­er FreeB­SD machine which did not exhib­it the prob­lems to more recent ver­sions of FreeB­SD (bina­ry search) until I encounter a prob­lem with the USB stick (or arrive at the same FreeB­SD ver­sion as the machine with the problems).