Steps to reproduce:

1. Open attached project "InputFieldMultilineBugDemo.zip"
2. Open scene "Master"
3. Run scene
4. Click on input field and press delete key to delete all characters
5. Type "ABC DEF GHI JKL MNO PQR STU" into input field and notice that text is multilined
6. Press enter key and notice that onle "ABC DEF GHI JKL" is displayed

Additional steps:
7. Using arrow key, move caret and notice that text quickly switches between single line and multi line once caret reaches invisible part of text

Reproduced with: 5.4.0f3, 5.5.0a5
Not reproducible: 5.3.6p1