Text caret not shown on focus in QLineEdit

Problem:

When the user initially clicks into QLineEdit, Qt sets the blinking insertion point text cursor to "blink off" state. Qt relies on the blinking action to make the cursor become visible a short time later.

Blink rate is a system-wide setting on Windows. If set to None, the initial cursor blink state never changes, and the cursor stays invisible. This gives the user no feedback that the QLineEdit has focus, and no indication where subsequent typing will enter text.

If the user now makes a move, such as entering a character, or using the arrow keys to move the (invisible) cursor, this forces the cursor to "blink on" state, and it becomes visible.

Repro:

Set Windows cursor rate:

Control Panel > Keyboard > Cursor blink rate > Set to None.

This problem can be demoed in the "Text Finder" demo application that comes with Qt. It also shows up in the Qt Creator itself – pick virtually any QLineEdit.

See attached video for a simple demo of this problem appearing in PCB software Eagle. The problem appeared in Eagle 7.3, which uses some version of Qt >5.1, but not in earlier Eagles, which used some earlier version of Qt.

Not the same, but probably related: https://bugreports.qt.io/browse/QTBUG-16627