[Groff] X in \A'X' isn't ignored - bug report?

[Steffen Nurpmeso]

Hello,

while trying to improve performance of mdocmx(7) on groff(1)
(without .hash request) further i'm now diversifying further via
.length+.substring (instead of only .length).  I am using \A'' so
that i can ensure the generated name can actually be used.
The (circumvented) problem is that, e.g.,

        $ cat > ~/tmp/t.tr <<-_EOT
        .if \A'du' \{\
        du ist ok.
        .\}
        .if \A'\[' \{\
        a bug?
        .\}
        huhu.
        _EOT

generates

  address@hidden roff.git]$ groff -Tutf8 < ~/tmp/t.tr
  <standard input>:5: missing `]'
  <standard input>:5: invalid component `a' in composite glyph name
  du ist ok.

That just can't be the intent, can it?  Is this a general parser
problem, i haven't looked yet..  Should i open a bug report?
Ciao,

--steffen