I was symptom free at the beginning of this current episode, but 3-5 days later I have experienced symptoms: mentally wiped, dull pain in lower back, a barely perceivable ache in groin area. My current thoughts: my problem (and possibly ours) is due to chronic prostatis. I have been tested for this years ago when I was relentlessly going to doctors looking for a cure. I had my PSA checked, secretion analyzed, semen ananlyzed, had more than one physical and had a camera jammed up my urethra for a look-see. Everything was "normal". But what I'm feeling now is telling me the tests were imperfect. Perhaps it is easier on a swollen prostate when you eat soluble fiber, less pressure against it. This of course would not explain girlwind's situation, but at the moment I am convinced.
I'm in the same situation: I was diagnosed for chronic prostatitis many years ago, before I even got aware of POIS (but it's not impossible I already was suffering from it). I underwent the same tests as you (already had two yearly PSA checks, close to but just under the normal limit), except for the camera up the urethra (that sounds scary). I did have several echographies showing cristallisations (English ?)
Maybe there is something worth investigating here.
Also take a look at Wikipedia's entry for chronic prostatitis: http://en.wikipedia.org/wiki/Chronic_prostatitis/chronic_pelvic_pain_syndrome