Is any simplified character also a traditional character? I don't mean traditional characters that weren't simplified, thus being the same in traditional and simplified.  

What I ask if there is any simplified character which in turn has the same form of another traditional character?  

I ask this because I was thinking if it was correct to mix simplified and traditional characters in the same text, and I guess it wouldn't be ambiguous at least if traditional and simplified character sets are disjoint sets.
There are plenty actually, mostly due to the merger of multiple traditional characters into one simplified character.  For example, the simplified character 后 maps to both traditional 后 (meaning 'queen') and 後 (meaning 'after' or 'behind').  Many of these mergers are listed in this Wikipedia article.