resizing toolbar buttons on device rotation?

[sneaky]

I'm a bit stumped how to resize custom UIBarButtonItem buttons on device rotation. I'm using the builtin toolbar of navigationitem and I roll out my own buttons like this:

	UIImage *btn0Image = [UIImage imageNamed:@"deleteButtonNormal.png"];
	UIImage *btn0ImageOver = [UIImage imageNamed:@"deleteButtonOver.png"];
	UIButton *b0 = [UIButton buttonWithType:UIButtonTypeCustom];
	b0.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
	b0.frame = CGRectMake(0, 0, 71, 44);
	[b0 setTag:kDeleteButton];
	[b0 setImage:btn0Image forState:UIControlStateNormal];
	[b0 setImage:btn0ImageOver forState:UIControlStateHighlighted];
	[b0 addTarget:self action:@selector(barButtonPressed:) forControlEvents:UIControlEventTouchUpInside];
	UIBarButtonItem *btn0 = [[UIBarButtonItem alloc] initWithCustomView:b0];

... (several more of the same..)

        NSArray *toolbarItems;
        toolbarItems = [[NSArray alloc] initWithObjects:btn0, flexSpace, btn1, fixedSpace, btn2, flexSpace, btn3, nil];
        [self setToolbarItems:toolbarItems];

When I rotate the device the buttons stay their original size. I have tried to play with the autoresizemask property of the UIbutton I create.
setting flexible height works and squashes the button a small bit, I need the width corrected too though. setting flexible width widens the buttons to take up the entire toolbar rather than scale proportionally.

Any suggestions what to do here??