Some characters do not display properly. In the range U+0400 to U+0402, the top part of the character is missing, which makes the first two characters look the same (Mac client) or the U+0400 character does not display at all (Windows client).
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A field that contains '\n', chr(10) or '\r' and is set as a Label widget does not display correctly. Those characters should create a new line, but instead display as a space.