Questions for EDS D1a users...

I used the EDS D1a that came with my DG-600 for the first time,
yesterday. This was a 6 hour flight in the 15 to 17.9K range. Up to
this point, all of my gliders have been equipped with continuous flow
systems and Oxymizer cannulas. This EDS setup was using the standard
XCR regulator, supplied tubing, EDS cannula, and a fresh 9V battery
installed. I set (and verified several times during flight) D5, which
is supposed to be a fully automatic mode of operation. According to the
manual, it should sense the start of inhalation and send a shot of
oxygen at that point. Instead, it seemed to be sending oxygen at fixed
intervals of a few seconds, then sounding an alarm (I assume the apnea
alarm) if I didn't happen to inhale just before the next shot. To keep
the thing happy, I had to sync my breathing with its cycle, and make
sharper than normal inhalations (i.e snort). By the end of the flight,
I was feeling signs of being mildly hypoxic. Questions:

1. Is this the way an EDS is supposed to operate, operator error, or
possibly a defective unit?
2. Why do EDS buyers insist upon getting those puny carbon fiber
cylinders (I used more than half the capacity in that one flight)?
3. Does anyone really like these things?

Marc