The average time interval between two consecutive occurrences of a new moon as seen by an observer on Earth, is 29.53 days. However due to the eccentricity of the lunar orbit around the Earth (and to a lesser degree, the Earth’s elliptical orbit around the Sun), this length of time can vary by up to seven hours.
According to calculations of moonsighting, up to three consecutive months of 29 days and up to four consecutive months of 30 days are possible, if sighting is limited to one location and not a big country. This is nothing unusual and happens quite often.
In Australia this year:
the likelihood of first sighting was on 14th September, giving 15/9 as the 1st of Dhul Hijjah, 1436.
the likelihood of first sighting was on 14th October, giving 15/10 as the 1st of Muharram, 1437.
the likelihood of first sighting was on 13th November, giving 14/11 as the 1st of Safar, 1437.
the likelihood of first sighting was on 13th December, giving 14/12 as the 1st of Rabi'al Awwal, 1437.
If the crescent was sighted as expected, then Dhul Hijjah would have been from 15/9 to 14/10 = 30 days,
Muharram would have been from 15/10 to 13/11 = 30 days,
Safar would have been from 14/11 to 13/12 = 30 days.