I'm forwarding a message sent to the Qt interest ML yesterday, because it concerns an issue I've encountered as well. For me, it occurred when stepping over a badly chosen expression like (from KDE4's Solid libs):
const int index = iface->metaObject()->indexOfProperty(d->property.toLatin1());
QMetaProperty metaProp = iface->metaObject()->property(index);
QVariant value = metaProp.isReadable() ? metaProp.read(iface) : QVariant();
QVariant expected = d->value;
It looks like a combination of an lldb issue that's aggravated by the fact Qt Creator uses Python to control lldb. I have however been able to get out of the situation by repeating "Abort Debugging" twice, and a killall -9 of the app I was debugging.
What's going on here? I presume the OP uses Apple's current LLVM tool chain, like I do.