Effect of widely differing volumes on ifile classification

I use ifile to classify all my emails, including the mailing lists I
subscribe to, and I tend to get a classification success rate of around
95-98%.

Recently, the rate, which had been consistent for some time, began to
plunge to about 50% and stayed there, until I deleted .idata and rebuilt
it from scratch, and it's now classifying better than before.  (Data
attached at bottom for completeness)

I'm wondering whether ifile's database got "overloaded" by having large
numbers of different volumes sent into different categories.  However,
if that were the case, then I'd have expected it to start classifying
emails into the mailing list categories rather than into other
categories.  This didn't happen - it actually started to misclassify the
mailing lists which receive all the volume.

Any ideas what could cause this "chaotic" effect?

jack


Date            Total   Incorrect       Percentage
----            ------- ---------       ----------
Thu Feb 20	160	8		95%
Fri Feb 21	189	7		96.2%
Sat Feb 22	164	2		98.7%
Sun Feb 23	45	3		93.3%
Mon Feb 24	85	1		98.8%
Tue Feb 25	136	2		98.5%
Wed Feb 26	171	7		95.9%
Thu Feb 27	167	23		86.2%
Fri Feb 28	164	44		73.1%
Sat Mar  1	166	58		65%
Sun Mar  2	131	29		77.8%
Mon Mar  3	129	17		86.8%
Tue Mar  4	195	43		77.9%
Wed Mar  5	279	62		77.7%
Thu Mar  6	180	50		72.2%
Fri Mar  7	257	9		96.4%
Sat Mar  8	157	28		82.1%
Sun Mar  9	106	0		100%    - didn't read email; no reclassification done
Mon Mar 10	93	48		48.3%
Tue Mar 11	172	76		55.8%
Wed Mar 12	160	51		68.1%
Thu Mar 13	131	4		96.9%   - regenerated .idata
Fri Mar 14	176	0		100%
Sat Mar 15	141	7		95%
Sun Mar 16	86	2		97.6%
Mon Mar 17	124	1		99.1%
Tue Mar 18	204	4		98%
Wed Mar 19	230	3		98.6%
Thu Mar 20	204	4		98%