Jakub Ouhrabka <jouh8664(at)ss1000(dot)ms(dot)mff(dot)cuni(dot)cz> writes:
> i observed strange behavior using hash index. is it a known bug?
No, not a *known* bug. Your message does not give sufficient info to
try to reproduce the problem, however. Could you try to come up with
a self-contained example?
regards, tom lane