This is true as of SunSpider-0.9.1, but has been true for longer than that, AFAICT. IMHO a benchmark suite should be deterministic. The variation caused by the Date.getTime() is large enough that it changes the amount of code is traced by TraceMonkey. I'd suggest hard-wiring a particular date+time into the test.
There may be some other non-determinism in SunSpider. string-base64 and string-validate-input both call Math.random(), for example.
Thanks for introducing version numbers for SunSpider, BTW, I think that's an excellent decision.
Thanks for the report. 1.9.1 is not released yet so we may still be able to fix this, but if not, we'll probably do so for a later version.
I think we'll probably reserve fixing the nondeterminism for SunSpider 2.0.