Bold typeface bug since cygwin-3.1.0

[Bruce Jerrick <bmj001 at gmail dot com>]

Problem:
Since cygwin-3.1.0-0.7 (test) and now with cygwin-3.1.0-1, in mintty
(mintty-3.1.0-1), text in bold typeface disappears after certain
commands are executed.

I have seen the problem under Windows 10 1903 and Windows 10 1903
Insider Previews, on x86_64 VMware virtual machines.
It does not happen under Windows 8.1 .  I do not know about Windows 10
1809; if it's really, really important I may be able to find out.
It does not happen if I revert to cygwin-3.0.7 .

To reproduce:
First, some preparation, for simplicity:
    Ensure that /etc/{bash.bashrc,profile} are the same as in
      /etc/defaults/etc/; also anything relevant in /etc/profile.d/ .
    Start mintty with an empty home directory (to eliminate any .bashrc,
      etc.)
    Set mintty background to pure white, foreground to pure black.
    The default TERM should be "xterm"; also happens with "xterm-color"
      and "xterm-256color".
     Set PS1='$ ',just to eliminate anything fancy it might output.
Then execute:
    echo -e "\e[1mBOLD\e[m"
    cygcheck --version | cat
or:
    /C/windows/system32/chkdsk.exe C: | cat

That causes the bold "BOLD" to disappear (replaced by whitespace).
(Also, bold blue (\e[1;34m) reverts to non-bold blue.)

The pipe is necessary to produce the bug; piping into 'head' does so
also.  But 'date | cat' does not cause the problem.  (Note: Those
executables feeding the pipe that produce the problem do not use
the Cygwin dll.  I have not yet explored this.)

All Cygwin packages are up to date as of x86_64/setup.ini with
setup-timestamp 1576533033 .
In particular:

    terminfo-6.1-1.20190727
    ncurses-6.1-1.20190727
    libncursesw10-6.1-1.20190727

Attachment: File cygcheck.out, from 'cygcheck -s -v -r'

-- Bruce Jerrick

Attachment: cygcheck.out
Description: chemical/gulp

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