The reasons I think this would be the case (just putting it out there) is simply the usual drivers... rates, inflation, tax, equity extraction, bank lending practices.. etc. All these things feed into supply/demand (not including pop. growth / demographic drivers) for the whole lot, not to mention sentiment which would also have a spillover effect at least to some extent.
It would be very irregular for units to fall and detached to rise for a protracted amount of time if previous data is correct.
