The Problem about QPlainTextEdit's copy-paste function

[timlong]

Hi all,
I find if I copy some words from QPlainTextEdit like "abc", I can paste those words success,
but if I copy other words (like "efg" )form other text editor, QPlainTextEdit always paste "abc", not "efg",
and I find if I copy words from other text editor first (not copy form QPlainTextEdit ), QPlainTextEdit can paste "efg" success.
Is anybody can help me find the problem?

Thanks

Tim

[timlong]

I find my console will print out
Warning: QClipboard::setData: Cannot set X11 selection owner for CLIPBOARD