Here are two images, only difference is the skin (Sand vs. Opus) The problem is in the TsBitBtn's (version 6.57) at the top:
[attachment=3801:TsBitBtnOK.jpg] [attachment=3800:TsBitBtnERR.jpg]
As you can see, three of the four glyphs do not show in the Opus skin (they also do not show in Bejing skin, but they do in Bejing Ext). Other skins in which the glyphs do not show are Acryl, Calcium, Neutral3, NextAlpha2, Office2003 (only if selected), Office2007Blue, Pulsar, Smoky, Snow Leopard, Soapsky Blue, Soapsky Lime, Terminal4Bit and Vista. You should be able to determine the common denominator between these skins.