See the below zul. Basically the assignation doesn't show up in the UI if you set the caption label before the image, until you next set the label again.

<panel title="Caption property ordering issue" border="normal" width="200px">
<caption id="c" label="Caption" image="/img/Centigrade-Widget-Icons/ArrowUp-16x16.png"></caption>
<panelchildren>
<vlayout>
If you click the below buttons in turn, the icon in the caption will not be updated correctly - it will lag behind by one assignment as it seems that if the label is set, the image is only subsequently updated when the label is set again.
<button label="Bad Left" image="/img/Centigrade-Widget-Icons/ArrowLeft-16x16.png"
width="125px" onClick='this.c.label="Left"; this.c.image="/img/Centigrade-Widget-Icons/ArrowLeft-16x16.png"'/>
<button label="Bad Right" image="/img/Centigrade-Widget-Icons/ArrowRight-16x16.png"
dir="reverse" width="125px" onClick='this.c.label="Right"; this.c.image="/img/Centigrade-Widget-Icons/ArrowRight-16x16.png"'/>

However if you click the below buttons in turn, the problem isn't there. because the image of the caption is being set before the label. The buttons above are doing it the other way around.
<button label="Good Left" image="/img/Centigrade-Widget-Icons/ArrowLeft-16x16.png"
width="125px" onClick='this.c.image="/img/Centigrade-Widget-Icons/ArrowLeft-16x16.png"; this.c.label="Left"'/>
<button label="Good Right" image="/img/Centigrade-Widget-Icons/ArrowRight-16x16.png"
dir="reverse" width="125px" onClick='this.c.image="/img/Centigrade-Widget-Icons/ArrowRight-16x16.png"; this.c.label="Right"'/>
</vlayout>
</panelchildren>
</panel>