[Groff] -me macro bug in centered block behavior?

[Dave Kemper]

Hi,

This looks to me like a bug, but I want to make sure I'm not doing
something wrong before I report it as such.  I'm using groff 1.21.
Here is my sample input file, which uses the -me macro set:

------------------------------
.pp
This is regular text.
This is regular text.
This is regular text.
This is regular text.
This is regular text.
This is regular text.
This is regular text.
This is regular text.
This is regular text.
This is regular text.
This is regular text.
This is regular text.
This is regular text.
This is regular text.
.(c
This is a centered block.
.)c
.pp
This is more regular text.
This is more regular text.
This is more regular text.
This is more regular text.
This is more regular text.
------------------------------

The output is not at all what you would expect from the documented
behavior of .(c and .)c.  What should be a free-standing block is appended
to the preceding paragraph, and the alignment of the last line of that
paragraph is a bit inexplicable.

Interestingly, putting a single empty line in the source code right
above the .(c macro call changes the output to what's expected, which,
as rendered in ASCII, is:

          This  is  regular text.  This is regular text.  This is
     regular text.  This is regular text.  This is regular  text.
     This  is regular text.  This is regular text.  This is regu-
     lar text.  This is regular  text.   This  is  regular  text.
     This  is regular text.  This is regular text.  This is regu-
     lar text.  This is regular text.

                         This is a centered block.

          This is more regular text.  This is more regular  text.
     This is more regular text.  This is more regular text.  This
     is more regular text.

Is there any reason this should behave so differently (and seemingly
illogically) without that extra blank line in the source?