mm problem with heading and short first paragraph

[Jennifer Sayers]

Dear Werner,

I seem to have found a bug in the mm macros.  If you have a heading
and then a paragraph which is one short line, a following paragraph
gets run into the first one (i.e. the .P in between doesn't take effect).

I have this bug on 1.19.3 but it doesn't appear in 1.18.1 that came
installed on my Linux system.

I have demonstrated the bug below using nroff, but I discovered it
using troff.

jen.

P.S. I will be away from my mail for several days.  I hope I have given
enough information.  If not, I will supply more when I return.

*****************************************************************************

$ cat show_bug.mm
.H 1 "A level one heading"
Paragraph with one short sentence.
.P
Another paragraph after the "dot P".
.H 1 "Another level one heading"
Paragraph with much more text the first sentence, which provokes proper
behaviour.
.P
Another paragraph after the "dot P".
$ 
$ /usr/local/bin/nroff -v
GNU nroff (groff) version 1.19.3
$ /usr/local/bin/nroff -c -mm show_bug.mm | col -b



                                   - 1 -



       1.  A level one heading

       Paragraph  with one short sentence.  Another paragraph after
       the "dot P".


       2.  Another level one heading

       Paragraph with much more  text  the  first  sentence,  which
       provokes proper behaviour.

       Another paragraph after the "dot P".


$ /usr/bin/nroff -v
GNU nroff (groff) version 1.18.1
$ /usr/bin/nroff -c -mm show_bug.mm | col -b



                                   - 1 -



       1.  A level one heading

       Paragraph with one short sentence.

       Another paragraph after the "dot P".


       2.  Another level one heading

       Paragraph  with  much  more  text  the first sentence, which
       provokes proper behaviour.

       Another paragraph after the "dot P".

$