I for one don't see what the argument is about.
Currently, if the taxation department know you are a non resident and are interested in your situation, you are liable to have your pension taxed at 30 odd percent - there is no argument there, that's an old and established provision in the taxation rules.
Luckily for the majority of expats this isn't currently enforced: however there is a proposal on the books to enforce it, how, when or whether this is passed and becomes the norm we currently don't know.
So, where is the argument - as an expat you are currently liable to pay this, although as stated it is ignored by the expats and the tax department don't seem to chase it up, however plans are in motion to change this - maybe it will happen, maybe not.
Time will tell, in the meantime, relax, enjoy your morning coffee, consider what the ramifications might be if the rules change or simply ignore it and hope for the best.