If you have ever pasted data into Calc in Open Office, you'll notice that any hyperlinks in the input data will be retained as hyperlinks rather than reduced to plain text. While this might be beneficial behaviour to some, it wasn't for me this afternoon. After a little digging around, I found that an easy way of removing the hyperlinks is by highlighting all the affected cells, right-clicking and choosing the Default Formatting option.
The associated CTRL + M shortcut (as seen in the Format menu) did not work for me.