On rebooting with the 20150503 packages, I get...
$this->bbcode_second_pass_code('', 'mmc0: Reset 0x2 never completed
mmc0: Reset 0x4 never completed
mmc0: timeout waiting for hardware interrupt')
...repeated endlessly. I realise that this is the sort of error that often comes with a dodgy SD card, but it's been fine up till now. I manually replaced the files in /boot with those from the previous 20150227 packages, and it works fine.
(Yes, I should probably have replaced the bootloader and firmware packages seperately, but I was in a hurry before going out.)
EDIT: Darn. Just realised you have a bugtracker. Anyway, I'll leave this here.