.sld blue labels in psse 35

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Hi there. I have a .sld and it works perfectly in psse 34. However, when I tried to open the same .sld in psse, some labels have blue background. I tried adjusting in Diagram Properties, Label Background -> clicked Transparent but the blue background still exists. Is this a bug when trying to open a older version .sld (psse 34) in psse 35. Are there any way to fix it?

Thanks!