If you add the following HTML text that contains two identical paragraphs in an HtmlTextBox, the first paragraph will contain the bold/strong text and the second will not. The specified font family doesn't have a font face for the bold text installed:
<p><span style="font-size: 9pt; font-family: arialmt"><strong>BILLING</strong> The total cost of the hearing aid(s), </span></p>
<p><span style="font-size: 9pt; font-family: arialmt"><strong>BILLING</strong> The total cost of the hearing aid(s), </span></p>
If you use two HtmlTextBoxes to display the two paragraphs, the second HtmlTextBox won't contain the bold text.
When you use a font family, which bold font face is installed, the HTML is rendered consistently.