The Wall Street Journal is reporting that Austin experienced one of the largest increases in apartment vacancy rates last quarter among major metropolitan areas. The vacancy rate, which jumped to 9.2% from 7.5%, is both high and rapidly growing --- a major problem for landlords and apartment developers.The problem with the rental market is rooted in recent history. For a long time, Austin has been one of the strongest rental markets in the country in terms of absorption and rent growth. Even as developers rapidly increased the number of units earlier in the decade, the market remain strong . . .