mintty overstrokes some fonts unexpectedly

[Lemures Lemniscati]

Hi!

mintty overstrokes some fonts unexpectedly.
https://gitlab.com/test.cases/mintty-test/-/tree/54ae800e695ecd1741851cab57320a9d0e95a6fd


How to reproduce

Setting mintty to use msgothic.ttc in 20pt, run a
following command.

====
perl -e '
binmode STDOUT, ":utf8";
print <<END;
01234567
\x{3042}\x{3044}\x{3046}\x{3048}
AaBbCcDe
\x{25cb}\x{25cb}\x{25cb}\x{25cb}
\x{3007}\x{3007}\x{3007}\x{3007}
\x{300c}\x{300e}\x{3010}\x{3012}
\x{300d}\x{300f}\x{3011}\x{3013}
\x{ff62}\x{ff63}\x{ff62}\x{ff63}\x{ff62}\x{ff63}\x{ff62}\x{ff63}
\x{ff71}\x{ff72}\x{ff73}\x{ff74}\x{ff75}\x{ff76}\x{ff77}\x{ff78}
END
'
====


I got a result mintty-sample-msgothic.png.
https://gitlab.com/test.cases/mintty-test/-/blob/54ae800e695ecd1741851cab57320a9d0e95a6fd/mintty-sample-msgothic.png

In the 4th line of the output, fonts (of u+25cb) were overstruck
unexpectedly.
And there are other characters also, which are similarly overstruck.


On the other hand, copying the result to a window of notepad.exe
displaying with msgothic.ttc in 20pt.

I got a result notepad-sample-msgothic.png, in which fonts were rendered
expectedly.
https://gitlab.com/test.cases/mintty-test/-/blob/54ae800e695ecd1741851cab57320a9d0e95a6fd/notepad-sample-msgothic.png


My cygwin environment is:

====
$ uname -srvmo; cygcheck -c mintty;
CYGWIN_NT-10.0 3.2.0(0.340/5/3) 2021-03-29 08:42 x86_64 Cygwin
Cygwin Package Information
Package              Version        Status
mintty               3.5.0-1        OK
====

Regards,

Lem