Performance inconsistency with setting text in edit control

We have several instances where the performance is extremely inconsistent when setting properties of a control.  Our 2 biggest areas of concern are edit controls and combo boxes with virtualized lists.  For the edit control I was able to isolate where the issue is.

This path takes from 2 seconds to over 2 minutes depending on the run.  Nothing changes on the test machine between runs.

WpfEdit myEditCtrl = GetEditControl();
myEditCtrl.Text = "New Text";

GetEditControl returns the real control, so no  searching is happening on setting the text.

The following code is so fast I am down to milleseconds

WpfEdit myEditCtrl = GetEditControl();
Mouse.Click(myEditCtrl);
Keyboard.SendKeys("New Text");