There are TWO behaviours.

Behavior 1
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1.Create a Frame with TextField.
2.Type five or six words in a single line (only one line should be there)
3.now the cursor is at the end of the line, now press the keys
  Shift and Up Arrow.
Expected Result: entire first line of text should be selected.
Actual Result: Nothing is selected.
4.move the cursor to begining of the line and press the keys Shift and Down Arrow.
Expected Result:entire first line of text should be selected.
Actual Result:Nothing is selected.
Note: the above scenario works for other lines after first line.

Behavior 2
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1.Create a Frame with TextField.
2.type around 10 lines of text
3.now the cursor is at the end of last line
4.Press Shift and UP Arrow keys continuously untill you reache last line
Expected Result: all text in all the lines should be selected.
Actual Result: First line some text or all the text will be left unselected
5.now move the cursor to begining of first line and Press Shift and DOWN Arrow Keys
  Actual Result: Last line some text or all the text will be left unselected

This Defect is reproducible in Solaris and only in 1.6.0 that too on Xtoolkit.
To reproduce the defect run the attached test and follow the above proceadure.