[Groff] Strange error messages from Groff 1.22.3

[Eli Zaretskii]

In some rare cases, Groff 1.22.3 emits strange (and quite cryptic for
this roff-ignorant curmudgeon) messages.  Examples:

  $ groff -man -t man1/chem.1 > cat1/chem.1
  <standard input>:4: `\c' is not allowed in a name
  mann1:550: `\c' is not allowed in a name

  $ groff -t -man man1/tbl.1 > cat1/tbl.1
  <standard input>:4: a node is not allowed in a name
  mann1:329: a node is not allowed in a name
  mann1:378: a node is not allowed in a name

I used the -t switch in these cases because that was suggested by
'grog'.  And at least tbl.1 has an explicit "'\" t" line at its
beginning to indicate that -t is in order.

Is this a known problem, or should I look into it?  (And what is that
"mann1" thing, btw?)

TIA