Actually there are two problems here:
1) Jasper one - if tag implements body tag support and sometimes body is empty
and sometimes not, then we may have next problem:
a)Tag uses body (bodyContent set)
b)Tag sent to pool (bodyContent set)
b)Tag uses empty body (old bodyContent set).
I've resolved this by setting bodyContent attribute to null before sending tag
to pool:
Generator.java, line 1440:
            if (ctxt.getOptions().isPoolingEnabled()) {
                //We must reset body before sending to pool if it was set before
                if (n.implementsBodyTag() && n.getBody() != null)
                {
                    out.printin(tagHandlerVar);
                    out.println(".setBodyContent(null);");
                }
                out.printin(n.getTagHandlerPoolName());
                out.print(".reuse(");
                out.print(tagHandlerVar);
                out.println(");");
            }

Second problem is with standart taglib: it uses needBody variable, but do not
resets it to false in StartTag ( and we may be NOT called release between uses)
Fix is: OutSupport.java, line 122:
    public int doStartTag() throws JspException {
      try {
        needBody = false;
        // print value if available; otherwise, try 'default'
        if (value != null) {
            out(pageContext, escapeXml, value.toString());
            return SKIP_BODY;
        } else {

This has been fixed for JSTL 1.0.3, currently available 
via the nightly builds.

*** This bug has been marked as a duplicate of 16069 ***