Hi, Zhen -
The implicit line breaks and "auto-wrapping" only occurs when the string contents being displayed or edited contains white space (spaces, tabs, new lines, etc.), as Andreas pointed out in his reply. If the data contains no white space, no wrapping or auto-adjustment of height will occur and data will display only as a single line of text. This is way Windows handles string data in single-line edit controls and PowerBuilder emulates this behavior in the DataWindow.
Below is a link to an example program in CodeXchange that shows you one way to change this behavior:
https://community.appeon.com/index.php/codeexchange/powerbuilder/280-string-break-adds-line-breaks-to-strings-by-analyzing-content#430
I'm not sure if it will help you with the particular issue that you experiencing, but you might consider taking a look at it.
Best regards, John