Craft hangs when saving any entry and brings Apache down

Question

Everything works fine on my local machine (OSX/MAMP PRO) but on my server (Digital Ocean LAMP stack on Ubuntu) saving an entry brings the whole thing down and I have to restart Apache before the site becomes responsive again. It doesn't seem to time out, it just never completes the save. Oddly, it does actually save the data so when I bring the server back up with service apache2 restart the changes are there.

Apache logs look like this:

zend_mm_heap corrupted zend_mm_heap corrupted [Mon Nov 03 11:44:55.395173 2014] [mpm_prefork:notice] [pid 16677] AH00169: caught SIGTERM, shutting down [Mon Nov 03 11:44:56.453282 2014] [mpm_prefork:notice] [pid 17116] AH00163: Apache/2.4.7 (Ubuntu) PHP/5.5.9-1ubuntu4.4 configured -- resuming normal operations [Mon Nov 03 11:44:56.453484 2014] [core:notice] [pid 17116] AH00094: Command line: '/usr/sbin/apache2' zend_mm_heap corrupted zend_mm_heap corrupted [Mon Nov 03 11:51:53.601504 2014] [mpm_prefork:notice] [pid 17116] AH00169: caught SIGTERM, shutting down [Mon Nov 03 11:51:54.577982 2014] [mpm_prefork:notice] [pid 17178] AH00163: Apache/2.4.7 (Ubuntu) PHP/5.5.9-1ubuntu4.4 configured -- resuming normal operations [Mon Nov 03 11:51:54.578223 2014] [core:notice] [pid 17178] AH00094: Command line: '/usr/sbin/apache2'

The zend_mm_heap corrupted bit looks like it could be something to do with it? I've tried increasing out_buffering as per this SO thread but it didn't help. I don't know where to even start with this, I've never experienced it before.

Apologies if this is a bit vague but this is the only place I can think of to ask — I've contacted P&T too.

EDIT: I've re-installed a new version of Craft in the same place on my server and, although the installation went 'Oops' I can actually log in and save entries so I don't think there's anything fundamentally wrong there.