If a custom TagErrorRenderer is used InputTagSupport.doEndTag() won't reset its state properly when the TagErrorRenderer's doAfterEndTag() method throws an exception. If the servlet container pools tags (like Tomcat) this could cause unexpected behaviour.

I think the following code in InputTagSupport:

    public final int doEndTag() throws JspException {
        int result = doEndInputTag();

        if (getFieldErrors() != null) {
            this.errorRenderer.doAfterEndTag();
        }

        if (this.focus) {
            makeFocused();
        }

        this.errorRenderer = null;
        this.fieldErrors = null;
        this.fieldErrorsLoaded = false;
        this.focus = false;

        return result;
    }

 should be changed into something like

    public final int doEndTag() throws JspException {
        try {
            int result = doEndInputTag();

            if (getFieldErrors() != null) {
                this.errorRenderer.doAfterEndTag();
            }

            if (this.focus) {
                makeFocused();
            }

        } finally {
            this.errorRenderer = null;
            this.fieldErrors = null;
            this.fieldErrorsLoaded = false;
            this.focus = false;
        }

        return result;
    }