odd Boss DD20 behaviour when reducing/increasing delay time

[Rainer Straschill <moinsound@googlemail.com>]

Has anyone done a throughout analysis how the Boss DD20 handles its
delay memory when first reducing, then again increasing delay time?
(Ted, I'm looking in your general virtual direction here ;).

The reason I'm asking. Just encountered some interesting behaviour
(and no, haven't tried to reproduce it, this is my last msg before
going to bed...):

Played the guitar into the DD20 - mode "smooth" from a memory slot,
preset to 23sec., reduced to a few seconds ("two bars") by taptempo
(via external FS), feedback about 60%.
I played some with that setting, then ended by tapping in a shorter
delay time (370ms) for that "unrounded multiply", had that fade out,
turned the delay off (left FS), set feedback to 100% and turned the
delay time back up to 23s with the depressed delay time knob ("time
advance").

During the turning up, I heard some of the DD20-glitching, then after
I had brought up the delay time again and released the time knob, the
last version of the delay contents before I did the shortening to
370ms became audible - it seemed that the part of the delay content
that was "multiplied away" had stayed in memory and thus got included
again after I turned the delay time back up.

Sooo...is this a known effect/feature? Can one make use of that in a
predictable manner (or, even better, in a non-predictable one)?

           Rainer