After testing, I think that KiXtart is behaving properly. It is your example that is causing your confusion. Let's examine the issue closer...
When your hit the Carriage Return, $myvar is not longer empty. It contains ascii character 13 (the CR).
The way you you output the text the text is printed
? 'Myvar: |'
Then you print ascii character 13 held in $myvar which returns the cursor to the front of the line. Then the last pipe character is printed over the "M" leaving you the text "|yvar: |".
The length($myvar) correctly prints 1.
You can see what character is in your variable by printing ASC($myvar).
