Default value not being displayed after upgrade to AEM 6.3 SP2

We're upgrading to AEM 6.3 SP2, and we noticed something strange.

The default value for textfield input fields we use in authoring dialogs is no longer displayed.

We define our components like this:

   <exampleField

        jcr:primaryType="nt:unstructured"

        sling:resourceType="granite/ui/components/coral/foundation/form/textfield"

        fieldDescription="This is an example input field."

        fieldLabel="Example input label"

        name="./exampleField"

        value="Default value"/>

I've traced the issue to this line of code in the initialization of the field super type: (/libs/granite/ui/components/coral/foundation/form/field/init.jsp)

     String value = cmp.getValue().val(cmp.getExpressionHelper().getString(cfg.get("value", "")));

I did some debugging:

- cmp.getExpressionHelper().getString(cfg.get("value", "")) is correctly returning the default value string "Default value"

- cmp.getValue().val(<defaultValue>) seems to return null

I suspect cmp.getValue().val doesn't return the default value when no value is found for the textfield in./exampleField.

Any idea where I can have a look at the internal workings of the ComponentHelper or Value class? Or any other reasons why the default value wouldn't be displayed?

Thanks in advance!

Oh, and my session is running the 5.7.6-CQ630-B0007 version of the com.adobe.granite.ui.commons artifact.