[Observium] Graphs not drawing after update to rev 7172

This afternoon I updated my installation to 7172 via svn. Since then, my graphs are being drawn blank (e.g. this one of the poller duration: https://dl.dropboxusercontent.com/u/3183918/pollergraph.png. Ignore the earlier gap, it's the one from about 1630 onwards I'm talking about).

I've done *./discovery.php -u* as normal and have manually run *./poller.php -h all*. I have checked /pollerlog and it doesn't appear to be running automatically by cron as usual.

Any ideas?

Tim