When clicking on a hotspot, the program mistakenly thinks an URL begins or ends too early if it contains a comma.
If you click to the left of the comma in, say, "http://www.test.com/a,b" the program will only try to match "http://www.test.com/a" as a URL. If you click to the right of the comma, it tries to match "b".
Solution: add a comma to the list of allowed characters.
About the parentheses: according to the RFC they are in fact valid URL characters, but they're obviously very uncommon. You are more likely to encounter parentheses enclosing a URL rather than being part of one, like "if you visit the website (http://www.test.com/test.html)...". Personally, if I click on that link I want to go to "test.com/test.html" and not "test.com/test.html)".
Thus, only alphanumerics, the special characters "$-_.+!*'(),", and
reserved characters used for their reserved purposes may be used
unencoded within a URL.