Strange rendering of one letter in on-line PDF reader

Hello,
My client, an advertising office, designs a magazine for on-line previewing based on PDF. Unfortunately, one single letter of the font is rendered with a strange shape around the letter. Accented letters A are affected (single A is fine). The letters look OK in InDesign as well as in Acrobat.

I did everything I could to avoid this problem: I changed direction of curves, I added a few redundant nodes, I did place the shape of Á to another glyph position. The Á is still rendered with the black shape.

Any idea what could be a source of this strange behaviour?




Thanks,
Filip