hmm a good 4dB level difference between L and R from 300Hz to 2kHz (Tyll's version).
20Hz = -2dB  drop off above 10kHz

And to think that some people are bothered by a 0.1dB channel imbalance from an amplifier  .

the GE measurement seems to differ a lot  (I know...) no channel imbalance there.
http://en.goldenears.net/10680
20Hz= 0dB drop off above 10kHz

The Russian guys also had a better looking FR
http://personalaudio.ru/raa/otchety/naushniki/beyerdynamic-dt-250-250-ohm/
BUT quite some differences between L and R also in the range of 4 to 5 dB which is (should be) more than obvious.
20Hz = -10dB no drop-off above 10kHz (a peak is even visible)

The Headroom plot looks a bit suspect .... roll-off in the lows starting from 100Hz and in the highs from 10kHz onwards ?
What's with that ? 20Hz = -15dB drop-off above 10kHz

I think the title of this thread thread is right on the money.... inconsistencies all over the place (channel imbalance) and or measurement/compensation errors.

HeadRoom and goldenears.net show the 80 Ω version (the former incorrectly labels it as 250, but it can be seen on the impedance graph that it is really 80). That may or may not be responsible for some differences.

The odd thing about the pair tested at InnerFidelity is that it has decent matching in the bass and treble range, where balance problems are otherwise more common.

Some of the old HeadRoom/InnerFidelity graphs do show incorrect bass response (such as too much roll-off, or a large notch somewhere between 50 and 100 Hz), due to seal problems and resonance in the HATS. These have been fixed since then.

and here is the IF link http://www.innerfidelity.com/images/BeyerdynamicDT250250.pdf
Wow, they measure pretty good for an old headphone. Now I wonder how they stack up against Tylls new favorite closed can... the NAD hp50. Tyll? Any thoughts? Or are the NADs much better overall?

I'm not Tyll but I own both the HP50 and DT250-250 now. The main difference is in the bass region, the HP50 seems to be more detailed and the bass goes deeper. It also gives a wider sense of space, so the imaging is better. Other than that I feel like both headphones are very similar. Will add more impressions when I get used to how the NAD sounds.

Just got Sforza's NAD's here and I feel the dt250-250s to be the better headphone overall by memory. The NAD is still nice and I still highly prefer them to the momentums.