WPF tab navigation issue

I ran into a small issue with WPF radiobuttons where pressing tab on the GUI will only select the radiobutton that is checked off but will skip other ones in the same button group. However, if I press Ctrl + Tab instead, then all radiobuttons in the same button group gets their turn to be selected.

Is this an in-built behaviour of WPF? If so, is there some way I can make Tab works like Ctrl + Tab for this instance? I've tried changing tabIndex, isTabStop, and various navigational properties but none worked.

Thanks.