The plugin does not sanitize and escapes some of its settings, which could allow high-privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed (for example, in multisite setup).
Add new Spacers and add payload ">
to Settings ยป Spacer ยป Add Spacers ยป New Spacer ยป Space Title and submit.