What do you expect?

I am surprised that others are surprised about criminal cases collapsing when evidence comes to light late in proceedings which undermines the prosecution's case.  This is evidence known to the prosecution which they are obliged under the rules to pass on to the defence, but have failed to do so until the last minute.  So, why the surprise?  If you think about it, the prosecution find themselves in a classic "conflict of interest" situation.  On the one hand, it is their job to build a case against the accused, and yet at the same time they are obliged to tell the defence about any evidence  they are aware of which harms that case.  Surely this aspect should be handled by an independent third party - a sort of modern Queen's Proctor maybe?