I understand that there are two problems with the blue pen, one which you found out, may have been caused if it was placed where light was on it for extended time, sunlight has a tendency to "set' the markings and it takes the soap to remove it, as you found. The other is when by regret water gets spilt on it and it all runs or fades out...In either case....it has been left up to Murphy's Law to determine which will work for you. :-) Glad to hear you did get it out. Best thing to do is use a scrap to test it on before use.