Digital BW, The Print

I have been printing on an Epson 1280, using the Piezography BW plug-
in and PiezoTone inks for over a year now. I have been very pleased 
with the results I have been getting, and have had hardly any 
problems at all....until now. I am pretty sure that this is a printer 
problem and not really a Piezography software or ink problem.

The problem I am having is sort of tricky to describe, but I will do 
my best. I have to start by asking a question: After completion of a 
print, the print head moves over to the "home" position at the right 
side of the printer, and then makes a kind of humming noise for about 
five seconds or so. What is this? Is it some kind of purge cycle or a 
cleaning cycle? What is happening here? (For clarification, I will 
refer to this as the "mystery cycle" from this point forward.) The 
1280 always does this after completion of a print; it also occurs 
(mid-print) when printing a large print (13x19). About 2/3 of the way 
through printing a 13x19, printing will stop, this "mystery cycle" 
will take place, then printing resumes.

Here is the problem. Whenever this "mystery cycle" occurs, 
immediately afterwards, the black position nozzles are clogged, and I 
mean badly clogged. How do I know this? After completion of a small 
print job, say a 5x7 or an 8x10, I do a nozzle check and discover 
that the black position is badly clogged, even though a nozzle check 
prior to printing was perfect! And the print is perfect, so the 
nozzle did not become clogged during printing. It leads me to believe 
that this "mystery cycle" that occurs after completion of the print 
job is what is actually clogging the nozzles. Also, when (as 
described above) this "mystery cycle" occurs about 2/3 of the way 
through a 13x19 print, the portion of the print which printed before 
the "mystery cycle" is perfect, but the remainder of the print job 
after the "mystery cycle" suffers from obvious micro-banding due to 
the clogged black-position nozzle. This is confirmed by a nozzle 
check after the print job is completed.

I am certain that this "mystery cycle" is causing the clogging. And 
is not an intermittent problem; the clogging is occurring after every 
print. The thing that has me puzzled is I can run a cleaning cycle 
and I always get a perfect nozzle check afterwards. Obviously, this 
is costing me lots of wasted ink due to way too many nozzle checks 
and cleaning cycles. And in the case of 13x19 prints, the bottom 1/3 
of the print, the portion of the print after the "mystery cycle" is 
ruined from micro-banding. Until I get this fixed I can't make any 
more 13x19 prints.

Does anyone know what this is? Has anyone else had this problem? And 
most importantly, how do I fix it?

Any help would be greatly appreciated.