Morphic: registering for doubleClick events on tite prevents window from being dragged? (Skylark theme)

Hello,

I thought I would implement the "double click on a window title to
close it" behavior. I use the skylark 2 theme from
http://www.comtalk.net/Squeak/87 on Squeak 3.9.

Skylark  adds a label area to the window where it puts buttons for
closing the window etc. Inside that method I added code to listen for
double click events:

SystemWindow>>initializeLabelArea
        "Initialize the label area (titlebar) for the window."

       .....

        "Make windows collapse and expand by double clicking on
        their title"
        labelArea
                on: #doubleClick
                send: #collapseOrExpand
                to: self.


Now I noticed that double clicking works, but I can no longer move the
window by dragging the title. What's going on? I am pretty
unexperienced in Morphic, so maye I am missing something basic here?


Cheers

Matthias

PS: Here is the whole method

initializeLabelArea
        "Initialize the label area (titlebar) for the window."
        label := StringMorph new contents: labelString;
                               
                                font: Preferences windowTitleFont
                                emphasis: (Preferences windowTitleFont isTTCFont
                                                ifTrue: [0]
                                                ifFalse: [1]).
        "Add collapse box so #labelHeight will work"
        collapseBox := self createCollapseBox.
        self useTheme
                ifFalse: [stripes := Array
                                                with: (RectangleMorph newBounds: bounds)
                                                with: (RectangleMorph newBounds: bounds)].
        "see extent:"
        self addLabelArea.
        self useTheme
                ifFalse: [labelArea
                                addMorph: (stripes first borderWidth: 1).
                        labelArea
                                addMorph: (stripes second borderWidth: 2)].
        self setLabelWidgetAllowance.
        self addCloseBox.
        self addMenuControl.
        labelArea addMorph: label.
        self wantsExpandBox
                ifTrue: [self addExpandBox].
        labelArea addMorph: collapseBox.
        self setFramesForLabelArea.
        "Make windows collapse and expand by double clicking on
        their title"
        labelArea
                on: #doubleClick
                send: #collapseOrExpand
                to: self.
        Preferences clickOnLabelToEdit
                ifTrue: [label
                                on: #mouseDown
                                send: #relabel
                                to: self].
        Preferences noviceMode
                ifTrue: [closeBox
                                ifNotNil: [closeBox setBalloonText: 'close window' translated].
                        menuBox
                                ifNotNil: [menuBox setBalloonText: 'window menu' translated].
                        collapseBox
                                ifNotNil: [collapseBox setBalloonText: 'collapse/expand window' translated]]