Invisible Bugginess

A programming language is too flexible when innocent typos result in different semantics.
C++ is too flexible.

Compare the following two. If I didn't know that I have messed around in those lines just five seconds ago, this would be a tough one.

if (!recon.importSlice (newFrameImage, QTime(), true)) {
...

if (!recon.importSlice (newFrameImage, QTime()), true) {
...