Summary and Info:
I have been finally able to reproduce bug #10773 . Here is the backtrack from gdb when runing pacman --debug -Syu:

(dumped)

:: Synchronizing package databases...
debug: using 'core.db.tar.gz' for download progress
error: failed retrieving file 'core.db.tar.gz' from ftp.sh.cvut.cz : Connection timed out
debug: using 'core.db.tar.gz' for download progress
debug: connected to ftp.heanet.ie successfully
debug: mtimes are identical, skipping core.db.tar.gz
core is up to date
debug: using 'extra.db.tar.gz' for download progress
error: failed retrieving file 'extra.db.tar.gz' from ftp.sh.cvut.cz : Connection timed out
debug: using 'extra.db.tar.gz' for download progress
debug: connected to ftp.heanet.ie successfully

Program received signal SIGSEGV, Segmentation fault.
0x00007fa9747929eb in mempcpy () from /lib/libc.so.6
(gdb) bt
#0 0x00007fa9747929eb in mempcpy () from /lib/libc.so.6
#1 0x00007fa974787cf3 in _IO_default_xsgetn_internal () from /lib/libc.so.6
#2 0x00007fa97477aa9f in fread () from /lib/libc.so.6
#3 0x00007fa9756e8018 in _alpm_downloadfiles_forreal () from /usr/lib/libalpm.so.2
#4 0x00007fa9756df701 in alpm_db_update () from /usr/lib/libalpm.so.2
#5 0x0000000000409d87 in ?? ()
#6 0x000000000040788c in ?? ()
#7 0x00007fa9747333f6 in __libc_start_main () from /lib/libc.so.6
#8 0x0000000000404449 in ?? ()
#9 0x00007fff7db10c58 in ?? ()
#10 0x000000000000001c in ?? ()
#11 0x0000000000000003 in ?? ()
#12 0x00007fff7db11538 in ?? ()
#13 0x00007fff7db11548 in ?? ()
#14 0x00007fff7db11550 in ?? ()
#15 0x0000000000000000 in ?? ()
(gdb)


Steps to Reproduce:
Pacman sometimes segfaults when syncing using slow and unstable internet connection