[IE] Inconsistent undo when inserting HR and page break

[Sa'ar Zac Elias]

The undo system is inconsistent when inserting HR and page break.

First scenario

• Load the editor and place the caret at the beginning of the text.
• Insert 2 HRs or page breaks.
• Click undo once.

A new paragraph is created and the caret moves into it.

• Click undo again.

The paragrpah is created and the caret goes to the expected location.

Second scenario

• Load the editor and place the caret at the beginning of the text.
• Insert 3 HRs.
• Click undo once.

The caret is vanished.

• Click undo again.

The caret is positioned near the HR.

• Click undo again.

The caret is positioned correctly.

[Garry Yao]

• First TC expired in trunk;
• Second TC is a DUP of #5614.