Problem with custom icon on toolbar (iPhone Beta 6 SDK)

Question

I created two custom icons, using transparency so they are white lines on a transparent background, to add to a toolbar at the bottom of the screen.
toolbar.barStyle = UIBarStyleDefault;
UIBarButtonItem *theItem = [[[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"MyImage.png"] style:UIBarButtonItemStylePlain target:self action:@selector(theAction:)] autorelease];
On the simulator, this shows properly a white icon on the grayish toolbar. On the device itself, it shows a white box the size of the icon. It still works.

Answer 1

Problem persists in Beta 7. However a workaround (which might have worked in Beta 6, I don't know) is this: use GIF files with transparency, rather than PNG files with transparency. These display properly on both simulator and device.