Candida albicans has an amazing ability to adapt to different stresses in the internal and external environments of the body. One of the ways in which it accomplishes this is through a process called aneuploidy. Aneuploidy is the ability to gain or lose genes at will, allowing an organism to adapt and continue growing. The use of medications can increase an organisms ability to adapt and the rate by which it adapts. In one experiment, radicicol-treated yeast cells grew better after being exposed to the antifungal fluconazole - http://the-scientist.com/2012/01/30/gain-a-chromosome-and-adapt/
That helps to explain why it becomes so problematic and why drugs don't work. Now we definitely know that drugs are making the situation worse. I read a while ago that antibiotics did the same thing with bacteria, made them adapt and grow antibiotic-resistant strains faster. Did you see this?