Hi Ryan - I for sure am not a developer, but I did find something in the release restrictions for 1.25 Lumira - see http://help.sap.com/businessobject/product_guides/vi01/en/lum_125_vp_en.pdf
Page 7:
"Thumbnail view may not correctly show an extension if it uses DIV as root container This is a known limitation in SAP Lumira that will be fixed in a future release.
Thumbnail view may not correctly show an extension if it uses external CSS files This is a known limitation in SAP Lumira that will be fixed in a future release"
Could this be related to your issue?
Tammy