Steps to reproduce the issue

1. Open modules/mod_login/mod_login.xml and add the following code:

<field
	name="colours"
	type="subform"
	formsource="modules/mod_login/colours.xml"
	layout="joomla.form.field.subform.repeatable-table"
	label="Colours"
	multiple="true"
	default='[{"colour":"#FF0000"},{"colour":"#008000"}]'
/>

2. Create a new file (modules/mod_login/colours.xml) and add the following code:

<?xml version="1.0" encoding="UTF-8"?>
<form>
	<fieldset name="colours" label="Colours">
		<field name="colour" type="color" label="Colour" />
	</fieldset>
</form>

3. In your Joomla administrator panel, open the Login module and you should see two default colours:
   

4. Delete both subform rows and click Save

Expected result

There should be NO colour fields shown.

Actual result

The field is reset back to the default values.