I was running Emacs in KDE, which can display several so-called
virtual desktops (or workspaces). I had made a new Emacs frame with
`C-x 5 2' and moved it to a different virtual desktop from the one in
which the initial frame was located. After finishing with the new
frame I typed `C-x 5 0' and not only did that delete the new frame,
but the initial frame was also gone, and Emacs dumped core. I then
started Emacs under gdb and ran it with -Q and repeated the above
actions, and Emacs promptly segfaulted. I repeated this two or three
times with the same result, and then suddenly I could not longer
reproduce it. But as I was composing this report, I tried it again,
and Emacs crashed again. So it appears to be reproducible, but not
reliably. What is common to all the crashes is that they only
happened when the deleted frame and the initial frame were on
different virtual desktops.