I am still not sure on how to solve this issue.
Hopefully the following code will help to locate the missing calls in order to resize the main window. Here is how I add the new widgets at runtime:
Qt Code: 
  1. lbltest = new QLabel(ui->tabw);
  2.     lbltest->setObjectName(QString::fromUtf8("lbltest"));
  3.  
  4.     lbltest->setAlignment(Qt::AlignCenter);
  5.     lbltest->setText("This is a test");
  6.  
  7.     ui->gl1->addWidget(lbltest,4,0,1,1);
  8.  
  9.     lbltest2 = new QLabel(ui->tabw);
  10.     lbltest2->setObjectName(QString::fromUtf8("lbltest2"));
  11.  
  12.     lbltest2->setAlignment(Qt::AlignCenter);
  13.     lbltest2->setText("test");
  14.  
  15.     ui->gl1->addWidget(lbltest2,5,0,1,1);
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This will work as expected and the mainwindow grows to accomodate the extra widgets.

Now I try to remove the labels with the following code:

Qt Code: 
  1. if (lbltest != NULL)
  2.     {
  3.         ui->gl1->removeWidget(lbltest);
  4.         delete lbltest;
  5.         lbltest = NULL;
  6.     }
  7.     if (lbltest2 != NULL)
  8.     {
  9.         ui->gl1->removeWidget(lbltest2);
  10.         delete lbltest2;
  11.         lbltest2 = NULL;
  12.     }
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I was hoping the mainwindow would shrink back to its original size, but instead, the original widgets expand into the additional space. At this point I can manually resize by dragging the border of the mainwindow back to the original size. Is it possible to achieve this programmatically?