I may be sticking my foot in the road apples here, but it seems to me the training was not effective, because the employee did not really understand the ramifications of not following the work instruction - contamination, causing defective material, possible life, health, safety issues, etc. I'm sure you all remember some brownnose in school who could parrot back all the textbook responses, but didn't know how to apply the information to real life situations.
I don't know that I would write this as a major, since it is one employee, not systemic. It is certainly an opportunity for improvement in the evaluation process of employee training. Is there a separate policy for willful disobedience? In an extreme case, with defense materials, for example, such activity by an employee is akin to sabotage.
Remind me some day to revisit the tale of ceramic heat shields coming off space shuttles because employees (ignoring specific work instructions)
at a supplier cleaned the tiles with a Scotch pad containing silicon which prevented the adhesives from working properly.