Please disregard.  It was a "user" bug.

In case you have a similar problem, here' s what I discovered:

When registering the control with Infopath, you follow a wizard where you
designate the bound field, the enabled property, etc..  The last thing it
asks is what datatype(s) you want to use your control for.  For my control, I
selected 'string' initially, but this presented a problem. For some reason,
carriage returns were not persisted in the control. They appeared initially,
but were missing when I reopened the file from disk.

So I had re-registered my control, but used the "field or group (any)"
option. This took care of the carriage return issue, but created the bug that
I indicated below.