Created attachment 330517 [details]
spreadsheet to demonstrate failed assertion ...... and segfault

Recipe:

1) Start a fresh instance of gnumeric, with no input file.
 Let it run in the background, to free up the controlling shell.

2) Start another instance of gnumeric, using the attached
 core-dump.gnumeric as the input file.
 You may wish to run this instance under gdb.

3) Select all of column A, or at least the top 3 cells.  Copy.

4) Switch to the other gnumeric.  Select cell A1.  Paste.

5) Observe that the paste does not complete.  Observe that the instance
 from whence we copied has crashed.  See the attached core-dump.logg file
 for details including a stack trace.

This is 100% reproducible chez moi.

==============

Background info:

:; gnumeric --version
gnumeric version '1.12.31'
datadir := '/usr/local/share/gnumeric/1.12.31'
libdir := '/usr/local/lib/gnumeric/1.12.31'

:; git log
commit e86ea3144fafb4b886c24b86f2bee0796220723c
Date:   Tue Jun 28 13:46:58 2016 -0400

:; uname -a
Linux asclepias 3.18.0+ #4 SMP Mon Jul 6 15:51:42 MST 2015 x86_64 x86_64 x86_64 GNU/Linux

:; lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 16.04 LTS
Release:        16.04
Codename:       xenial