Docbook parser fails to support Italic syntax nested inside Bold syntax

.#-----------------------------------------------------
.expect|event/1.0
.#-----------------------------------------------------
beginDocument
beginParagraph
onWord [This]
onSpace
onWord [is]
onSpace
beginFormat [BOLD]
onWord [bold]
onSpace
onWord [and]
onSpace
beginFormat [ITALIC]
onWord [italic]
endFormat [ITALIC]
endFormat [BOLD]
endParagraph
endDocument
.#-----------------------------------------------------
.inputexpect|docbook/4.4
.#-----------------------------------------------------
<article><para>This is <emphasis role="bold">bold and <emphasis>italic</emphasis></emphasis></para></article>