A relative url for a background-image in the presence of an empty href attribute of a base tag will cause an unrecoverable error (and a freeze) in Amaya every time.

If run from console, see

*** glibc detected *** free(): invalid next size (fast): 0x09984150 ***
*** Amaya: Irrecoverable error ***

That is, Amaya 9.1 Windows and Amaya 8.8.1 and 8.8.5 on Linux, on an IBM T42p.