Foreach syntax + generics, Possible compiler bug?

Question

I'm encountering an odd problem trying to use generics and the foreach (colon) syntax. The code in question:
for (Iterator<String> it = col.getParameterNames().iterator(); it.hasNext();) {}
for (String paramName : col.getParameterNames()) {}col is an instance of an inner class of the class whose method this code snippet is from, getParameterNames has the signature:
public Set<String> getParameterNames();
The first line, using the Iterator<String> explicitly, compiles fine. The second line, when present, raises the compiler error:
found : java.lang.Object
required: java.lang.String
for (String paramName : col.getParameterNames()) {
I cannot seem to reliably reproduce this situation in other (simpler) classes I write, but this one in particular seems to trigger it. Is it possible this is a compiler bug, or might there be something I'm doing incorrectly that I'm missing? Are my expectations about how the second line should work incorrect? It seems to in other circumstances...
javac is 1.6.0_01. Any ideas?

Answer 1

Here is a quick update, I'm more inclined to think of this as bad behavior now.
This code compiles:
public class Test {
Vector<InnerTest> inners = new Vector<InnerTest>();
    public class InnerTest {        
       public Set<String> someSet() { return (new HashMap<String,String>()).keySet(); }
    public Test() {
        for (InnerTest it : inners) {
            for (String s : it.someSet()) {        
}however, the following does not:
public class Test {
Vector<InnerTest> inners = new Vector<InnerTest>();
    public class InnerTest<P> {        
       public Set<String> someSet() { return (new HashMap<String,String>()).keySet(); }
    public Test() {
        for (InnerTest it : inners) {
            for (String s : it.someSet()) {        
}Again, the problem might be with my expectations (I haven't gone through the specifications yet with this in mind), but I can't fathom how or why the unused parameter would make a difference in that method's tpye matching.