Its sounds like its most likely a strain related feature. Some strains of cannabis will flower without a change in light cycles. Some strains that originate closer to the equator dont experience a change in the cycles, therefor they flower basically when ever they feel its time...

However, this is very odd for a BigBud to do something like that. Are you 100% positive its a BigBud decendant? It could be mixed...Other than the strain being the case i cant think of any other explanation...

Did you top it? Toppin any cannabis plant usually causes it to flower...