cursor disappears in QLineEdit when application loses then regains focus from an alt+tab on OSX

When the contents of a QLineEdit are selected entirely and the user Command-Tabs to a different application, the selection remains highlighted upon Command-Tabbing back, but the blinking cursor is gone.

Tested with two applications (one with a custom derived QLineEdit, one with a "standard" QLineEdit) and in both circumstances bug can be demonstrated:

1. Type text in QLineEdit
2. Highlight the text
3. Command-Tab to another application
4. Command-Tab back to test application

The result is a "missing" cursor. Editing continues as usual, but the cursor becomes invisible. Tabbing between QLineEdit fields will usually fix the cursor display, but toggling a QComboBox will restore the cursor.

This behaviour did not exist in Qt 4.5.