Hi PSR, interesting discussion, thanks for posting.
given a speed restriction of 270kts or less when he was cruising at FL400 and at least 30 miles from TOD. The pilot flew at mach 0.85 (or something similarly high) until FL230! IAS was around 340kts if I remember correctly. His excuse was he hadn't transitioned to IAS yet. This too makes no sense to me. 270kts or less is 270kts or less. It applies at any level, even when flying with reference to mach
We often receive "Mach xx and xx KT on conversion", so I can see how a tired or otherwise busy pilot could misinterpret the instruction - despite the obvious clarity in your request.
At my UK base we are very limited in descent by a mid-level restriction during arrival which often requires a higher speed down to around FL60 to get below the terminal limits. What a number of us cannot understand is why we are given standard speeds with 2 to 4 thousand to go before we are passed to approach, at which point the speed restriction is removed. (We of course appreciate that there may be other influencing factors that we cannot know of from the flight deck).
AD