Created attachment 119579 [details]
trace of Writer via --backtrace argument.
I believe this could have something to do with changes to the gtk filechooser, but I am not certain.
Fresh install of Arch Linux along with GNOME 3.18.1 and LibreOffice 126.96.36.199.
Problem was not present when running GNOME 3.16.
Happens in all applications after selecting "Save As.../a Copy" but before the filechooser dialog appears.
Opening files functions.
Problem can be worked around by using SAL_USE_VCLPLUGIN=gtk instead.
*** This bug has been marked as a duplicate of bug 94936 ***