From a UK company Boeing MEL:
9. The MEL does not anticipate the effects of combinations of apparently unrelated unserviceabilities or allow for situations where systems are made inoperative for special purposes such as demonstration, test or crew training. Other provisions may apply to positioning of ferrying flights but these may not necessarily be included in the MEL.
10. The decision to operate the aircraft with multiple unserviceabilities should only be made after due consideration of possible inter-related or additive effects