Although your portora bloom shows an exceptionally abbreviated spathe, I, too, have seen them come out with spathes much smaller than the spadix. I have not focused on this phenomenon but I suspect it may be related to the wintertime activity (or lack thereof). You kept yours going in winter so that gave the plant a chance to initiate flower primordia, but the cooler nights (cooler than summertime) may also have caused parts of the developmental process to stall somewhat. Leaves get smaller in the winter due to less sunlight and cooler temps (I'm talking Florida here) so since the spathe is, developmentally speaking, a modified leaf, it makes sense that what affects the leaves would affect the spathes as well.
Hope this helps,
LariAnn
