Try this instead of right clicking and clicking copy URL. Drag your pointer over the source text to high lite it then right click and click copy then paste it in to your sources section in edit. Post a link to the source and a example so we can see it as you have. Copying the URL will only let you enter the URL under sources it will not actually insert the text of the source. See how to add sources below.
Categories: WikiTree Help | Sources
A source is the identification of where you obtained information. Sources are critically important for genealogy. Some even say that genealogy without sources is mythology.
You must include your sources when you put information on WikiTree. It's in our Honor Code.
For more background on why sources are important and how to record them during your research see "Source, Source, Source" in Getting Started With Genealogy or Cite Your Genealogy Sources on About.com.