CRITICAL warnings (?and segfault ?) associated with AxisLine

Recipe: Open the attached file. Even before doing anything else, while the spreadsheet is still unmodified, if I ask to save the file (control-S) I observe CRITICAL warnings:

** (/usr/src/gnome/gnumeric/src/.libs/gnumeric:32588): CRITICAL **: 07:42:13.833: gnm_expr_top_as_string: assertion 'GNM_IS_EXPR_TOP (texpr)' failed

** (/usr/src/gnome/gnumeric/src/.libs/gnumeric:32588): CRITICAL **: 07:42:13.833: gnm_expr_top_as_string: assertion 'GNM_IS_EXPR_TOP (texpr)' failed

Also if I open the graph properties and click on the X-axis AxisLine, even without changing anything, I observe multiple CRITICAL warnings.

Both of the above are 100% reproducible chez moi.

critical-crash.gnumeric

In addition: Sometimes I observe a segmentation fault. I do not yet know how to reproduce this reliably. Working on it.

A console log is attached.

critical-crash.logg

Platform: This is observed using gnumeric compiled from freshly-pulled git sources.

:; uname -srmo
Linux 4.19.42+ x86_64 GNU/Linux

:; lsb_release -a
LSB Version:	core-9.20170808ubuntu1-noarch:cxx-3.0-amd64:cxx-3.0-noarch:cxx-3.1-amd64:cxx-3.1-noarch:cxx-3.2-amd64:cxx-3.2-noarch:cxx-4.0-amd64:cxx-4.0-noarch:cxx-4.1-amd64:cxx-4.1-noarch:desktop-3.1-amd64:desktop-3.1-noarch:desktop-3.2-amd64:desktop-3.2-noarch:desktop-4.0-amd64:desktop-4.0-noarch:desktop-4.1-amd64:desktop-4.1-noarch:graphics-2.0-amd64:graphics-2.0-noarch:graphics-3.0-amd64:graphics-3.0-noarch:graphics-3.1-amd64:graphics-3.1-noarch:graphics-3.2-amd64:graphics-3.2-noarch:graphics-4.0-amd64:graphics-4.0-noarch:graphics-4.1-amd64:graphics-4.1-noarch:multimedia-3.2-amd64:multimedia-3.2-noarch:multimedia-4.0-amd64:multimedia-4.0-noarch:multimedia-4.1-amd64:multimedia-4.1-noarch:printing-9.20170808ubuntu1-noarch:qt4-3.1-amd64:qt4-3.1-noarch:security-9.20170808ubuntu1-noarch
Distributor ID:	Ubuntu
Description:	Ubuntu 18.04.4 LTS
Release:	18.04
Codename:	bionic

:; ../src/gnumeric --version
gnumeric version '1.12.48'
datadir := '/usr/src/gnome/install/share/gnumeric/1.12.48'
libdir := '/usr/src/gnome/gnumeric'

:; git log
commit 006a1b200e792d61c3adcdb5f9f3fb865a515d55
Date:   Mon May 11 08:58:34 2020 +0000