Windows forms control behaves differently in WPF app

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C#

WPF

Fast Colored TextBox for Syntax Highlighting[^]

I'm using the above control for a custom syntax highlighter. I'm trying to dynamically update the styles used. When I look at the example, it changes color when the TextChangedDelayed event is fired, but when I implement similar code, it changes color and then changes the text:

Example:

fctb.Range.ClearStyle(KeywordsStyle, FunctionNameStyle);
            //highlight keywords of LISP
            fctb.Range.SetStyle(KeywordsStyle, @"\b(and|eval|else|if|lambda|or|set|defun)\b", System.Text.RegularExpressions.RegexOptions.IgnoreCase);
            //find function declarations, highlight all of their entry into the code
            foreach (Range found in fctb.GetRanges(@"\b(defun|DEFUN)\s+(?<range>\w+)\b"))
                fctb.Range.SetStyle(FunctionNameStyle, @"\b" + found.Text + @"\b");

My Code:

fctb.Range.ClearStyle(FnDynamic, VarDynamic);
            //find function declarations, highlight all of their entry into the code
            foreach (Range found in fctb.GetRanges(@"\bprocess\s+(?<range>\w+)\b"))
                fctb.Range.SetStyle(FnDynamic, @"\b" + found.Text + @"\b");
            foreach (Range found in fctb.GetRanges(@"\bvariable\s+(?<range>\w+)\b"))
                fctb.Range.SetStyle(VarDynamic, @"\b" + found.Text + @"\b");
            foreach (Range found in fctb.GetRanges(@"\bfor\s+(?<range>\w+)\b"))
                fctb.Range.SetStyle(VarDynamic, @"\b" + found.Text + @"\b");

I implement this control using System.Windows.Forms.Integration.WindowsFormsHost, so it should work the same (I think). Instead, it seems like the same event (TextChangedDelayed) is firing at different times in WPF (Before the text is written to the screen) than in windows forms (After the text is written to the screen an the user has stopped typing).

Any ideas as to why this would happen?

Thanks!