I've just noticed that this only happens if you have your desktop icons to the maximum supported size, which is greater than "Extra large icons". You can reach that icons size with CTRL+mouse wheel in.
I am afraid no changes will be made to Fences anytime soon regarding your issue. In the meantime, we would suggest not using icon sizes beyond 'Extra Large Icons' where the issue is not present.
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Sean Drohan
Stardock Customer Service Manager