From my experimentation, that is not the behavior I got.

I built a form with two tabs controls, each with two pages. In the first tab
control, I put two edit box on its second page, while on the second tab
control, I place a UC having, itself, three edit box. I added two command
button, their click event selecting the tab of the second page:

       private void button1_Click(object sender, EventArgs e)
       {
           tabControl1.SelectTab(1);
       }

       private void button2_Click(object sender, EventArgs e)
       {
           tabControl2.SelectTab(1);
       }

Running the Windows application, what I got is : when I click the button AND
the selected page was not the one selected, then the first control of the
said page get the control. Whhtever it is an UC or another control. If I
click on the button a second time, while the page to be selected is already
the one 'displayed', the focus stays on the button  rather than moving to
the first control of the page (and next, I can navigate through the control
of the form with the keyboard, as usual, in such situation).

So, in *this*  scenario, to get the same effect, anytime, I can use:

       private void button1_Click(object sender, EventArgs e)
       {
           tabControl1.SelectTab(1);
           button1.Select();
       }

       private void button2_Click(object sender, EventArgs e)
       {
           tabControl2.SelectTab(1);
           button2.Select();
       }

Hoping it may help,
Vanderghast, Access MVP