Struts problem with InsertTag

I'm having an issue with websphere 5.1 and tiles not rendering correctly with large amounts of data. Somehow the data seems to be interrupted randomly and doesn't produce the full html that I'm expecting. To me it sounds like a problem with buffers and flushing and eventually I found a workaround.
I makde a change in method doEndTag of InsertTag from this:

// include requested component.
if (flush) {
pageContext.getOut().flush();
}
doInclude(page);

to this:

if (flush) {
pageContext.include(page);
} else {
TilesUtil.doInclude( page, (HttpServletRequest)pageContext.getRequest(),(HttpServletResponse)pageContext.getResponse(),pageContext.getServletContext());
}

Is this purely a Websphere issue or is anyone else experiencing similar problems with uncomplete data?

/C a Struts newbie