Hi,
On P.257 of "X Toolkit Intrinsics Programming Manual"
(Volume Four Motif Edition, OSF/Motif 1.2 Edition) it says
all b events are discarded with a translation table:

a,b : something()
: else()

Why? Was there a design decision to do that, or was it just
a quirk that a particular algorithm happen to have?

It says b events will work as expected with:

a,b : something()
b : else()
: else()