Hello,
I have two (separate) DataObject subclasses, each containing a $has_one like this:

private static $has_one = array(
	'PageLink'=>'SiteTree',
	'Picture'=>'Image'
);

and in getCMSFields,

TreeDropdownField::create('PageLinkID', 'Optional page to link to', 'SiteTree'),

but in the CMS, it always appears as readonly (i.e. just the name of what it's linking to, and viewing source shows "treedropdownfield_readonly"). Even when I explicitly make it not readonly afterwards.
What's really weird is that if I change $has_one to

private static $has_one = array(
	'PageLink'=>'SiteTree',
	'Dummy'=>'SiteTree',
	'Picture'=>'Image'
);

it is no longer readonly (but creating a TreeDropdownField for Dummy is readonly). Any ideas what the problem could be? This is driving me partially insane.

On a secondary note, having

'Picture.SetWidth(100)'=>'Picture',

in my $summary_fields doesn't make it display, but using a custom method does. Is this related?

All help is greatly appreciated.