It's not an issue of copying the link right or wrong. When you put the URL into a post, most forum software parses it, changes it from a URL into the page name & links that page name to the URL. The issue is with the forum software doing the parsing. My bet is it has some issues with punctuation. Probably erroneously parsing a comma as an escape character or delimiter of some sort.
It's also VERY common for the & character and quotes to get messed up when copying & pasting for similar reasons. Microsoft word in particular changes a pair of double quotes into an upside down pair & a right side up pair for some reason. At least one of those rarely turns out well when pasted into a web form & parsed by software that is expecting standard ASCII characters.