“No base glyph” in Glyphs Viewer

I can’t get glyphs built from components to show up in Glyphs Viewer. For example, the O and the acutecomb each display fine by themselves, but Oacute displays two triangles that say “no base glyph.” Everything shows up fine in the Preview Area and Preview Panel. Am I doing something wrong?

What do you mean by ‘Glyphs viewer’?

iPad app, sorry.