I change to contextMenuEvent:

Qt Code: 
  1. void MainTextEdit::contextMenuEvent(QContextMenuEvent *event)
  2. {
  3.         if (this->textCursor().selectedText().isEmpty() == true) // if nothing selected
  4.         {
  5.             QTextCursor cursor = cursorForPosition(event->pos());
  6.             cursor.select(QTextCursor::WordUnderCursor);
  7.             if (!cursor.selectedText().isEmpty())
  8.             {
  9.                 QString strText = cursor.selectedText();
  10.                 int iPos = cursor.position() - cursor.block().position(); // cursor.positionInBlock()
  11.  
  12.                 cursor.select(QTextCursor::BlockUnderCursor);
  13.                 QString strBlock = cursor.selectedText().trimmed();
  14.                 QStringList strlBlock = strBlock.split(" ");
  15.  
  16.                 QString strWord = strlBlock[1];
  17.  
  18.                 // channel
  19.                 if (strText.at(0) == '#')
  20.                 {
  21. ...
  22.                     QMenu *menu = new QMenu(strChannel);
  23. ...
  24.                     menu->popup(event->globalPos());
  25.                     return;
  26.                 }
  27.  
  28.                 // nick
  29.                 if ((iPos > 11) && (iPos < 11+2+strWord.length()))
  30.                 {
  31. ...
  32.                         QMenu *menu = new QMenu(strNick);
  33. ...
  34.                         menu->popup(event->globalPos());
  35.                         return;
  36.                 }
  37.             }
  38.         }
  39.  
  40.     QTextEdit::contextMenuEvent(event);
  41. }
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but still sometimes vertical scroll bar stops ...