This is not an EasyABC problem. The "issue" is with abcm2ps. Only a limited number of special characters are supported out-of-the box by abc2mps. This includes most common accented characters but not left and right single or double quotes (or the Euro symbol). You need to include a %%glyph directive at the beginning of your abc for each uncommon special character you are using. Specifically in this case the line
%%glyph 2019 quoteright
The display from EasyABC looks fine as it is rendering an SVG file and the SVG renderer can cope with all special characters (provided they exist in the font).
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This is not an EasyABC problem. The "issue" is with abcm2ps. Only a limited number of special characters are supported out-of-the box by abc2mps. This includes most common accented characters but not left and right single or double quotes (or the Euro symbol). You need to include a %%glyph directive at the beginning of your abc for each uncommon special character you are using. Specifically in this case the line
%%glyph 2019 quoteright
The display from EasyABC looks fine as it is rendering an SVG file and the SVG renderer can cope with all special characters (provided they exist in the font).