Steps to reproduce the issue

Use the following subform field in a form

<field name="field-name" type="subform"
    label="Subform Field"
    multiple="true">
    <form>
        <field name="fieldx" type="list"
            label="Foo">
            <option value="0">No</option>
            <option value="1">Yes</option>
        </field>
        <field name="fieldy" type="text"
            label="Example Text"
            showon="fieldx:1"
        />
    </form>
</field>

Click to add a new item

Expected result

fieldy must show up only when we select Yes in fieldx

Actual result

fieldy shows up and ignores the showon rule.