keystroke echoing oddity

[Evil Boris]

[This is unimportant, but odd.]
This applies (I think) every time I type a multi-key sequence
incompletely.  Easy example: numeric prefix in RMAIL, or in gnus
summary buffer.

If I type, say 1234 very *slowly*, I see in echo area:
1-
1 2-
1 2 3-
1 2 3 4-
If I type the first two keys with less of a delay, I get
12-
12 3-
12 3 4-

Notice the absence of the space between 1 and 2.  The difference seems
to be related to whether or not I wait for the first character to be
echoed. 

--Boris