Hello,
It looks like the lexer source was rebuilt since that original fix, when we added some more advanced features to the advanced XML syntax language. This was noticed again in the 2016.1 timeframe and was resolved in v16.1.0632.
As for a workaround in 2015.1, that might be tricky. The fix was that the pattern for the main LexicalPatternGroup in the StartTagAttributeDoubleQuoteValue lexical state was changed to "[^\\\"]+", and the pattern for the main LexicalPatternGroup in the StartTagAttributeSingleQuoteValue lexical state was changed to "[^\\\']+". For the XML lexer in the add-on, we actually use the XML.langproj in the sample project and code generate the XmlLexer.cs class from that. You could change the XML.langproj yourself per above using our Language Designer, then use it to code generate a new XmlLexer.cs. After you create a normal instance of XmlSyntaxLanguage, do this call:
language.RegisterLexer(new MyXmlLexer(new XmlClassificationTypeProvider()));
That will get your updated lexer (assuming you renamed the class that was generated as MyXmlLexer) used for syntax highlighting. The XmlParser also creates a lexer instance though. You'd have to make a MyXmlParser class that inherits XmlParser and overrides this method:
public override ITokenReader CreateTokenReader(ITextBufferReader reader) {
return new XmlTokenReader(reader, new MyXmlLexer(new XmlClassificationTypeProvider()));
}
Then back like above, you'd need to register this new parser in place of the old one:
language.RegisterParser(new MyXmlParser());
After you do those things, I believe it will work. But again, the latest 2016.1 versions also have it working already.