Strange iostream problem when porting app to qt 5.3

I am using QCreator 3.1.2 on windows 7 when porting an old application to QT 5.3. After numerous changes I found on the internet, it now compiles and runs. But one class contains #include <iostream> which QCreator flages with "No such file or directory". However when I comment it out the statement "std::cout" contained in a method does not compile. It fails with the error "cout not in std". Put it back in and, even though QCreator can't find iostream, everythng works! I am concerned because it seems like something is configured incorrectly. I just recently installed Qt 5.3/QCreator 3.1.2 and, as far as I know, I am using only the libs and includes that came with Qt. If there is another minGW on my system, I don't know where it is.

After making other changes. This problem went away.

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After making other changes. This problem went away.

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And that doesn't make you worry a little bit about why it went away?