I have recently rented out two in this area with no troubles. My PM told me that she can't get enough stock. Is your IP a very nice one, meaning it is too expensive for the demographic, perhaps? Or maybe has unusual features (like the coin-op laundry of another poster) which makes it harder to lease?
For instance, we had one with a Granny Flat. Renters were reluctant as there was no fence between the flat and the house. Put a fence in place and BAM! It was gone.
Another that I noticed (because it was similar to the above) was a house that was for lease with a flat. They wanted to lease them both to the same tenant and were asking over $500pw in an area that $300 for a house is expensive. This stayed on the market for some time. Eventually they decided to rent house and flat seperately. I believe they have been tenanted now.