Setting a stylesheet that changes the margin or padding will cause QTextEdit to draw the background using QPalette::Window instead of QPalette::Base.

Here is a code snippet that will show the issue:

#include <QtGui>

int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QTextEdit edit;
edit.setStyleSheet("QTextEdit

"); // Wrong background
//edit.setStyleSheet("QTextEdit

"); // Wrong background
//edit.setStyleSheet("QTextEdit

"); // OK
edit.show();
return app.exec();
}