emacs-X11 freezes with mouse cut and paste

["Rockefeller, Harry" <Harry.Rockefeller@flightsafety.com>]

CYGWIN_NT-6.1 HARRYR-PC 3.0.4(0.338/5/3) 2019-03-16 09:50 x86_64 Cygwin
GNU Emacs 26.1

How this happened.
It had happened twice before but appeared to be intermittent.
This time it happened I had copied a line from an xterm, including the [return].
Moved mouse to emacs window and using the middle mouse button attempted to paste the copied text.
It didn't paste and now emacs is frozen; not responding to keyboard or mouse.

In xterm window I entered
Gdb /usr/bin/emacs-X11.exe
Gdb told me it read the symbols.
(gdb) info source
Current source file is /usr/src/debug/emacs-26.1-1/src/emacs.c
Compilation directory is /usr/src/debug/emacs-26.1-1/src
Located in /usr/src/debug/emacs-26.1-1/src/emacs.c
Contains 2676 lines.
Source language is c.
Producer is GNU C11 7.3.0 -mtune=generic -march=x86-64 -ggdb -O2 -fopenmp -fstack-protector-strong --param ssp-buffer-size=4.
Compiled with DWARF 2 debugging format.
Does not include preprocessor macro info.
(gdb) list
660           emacs_perror ("Write error to standard output");
661           _exit (EXIT_FAILURE);
662         }
663
664       /* Do not close stderr if addresses are being sanitized, as the
665          sanitizer might report to stderr after this function is
666          invoked.  */
667       if (!ADDRESS_SANITIZER && close_stream (stderr) != 0)
668         _exit (EXIT_FAILURE);
669     }

I am not familiar with using gdb this way.  There is no "frame", no "info local", no stack.
If there is something else I can provide please let me know.

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