textarea problem when checking for number of words entered

Using OPS nightly build from 3-4 days ago with XForms NG.

I have a textarea in my form and I want to restrict users from being able to paste more that certain number of words. I have adapted the registration form from the OPS examples for my purposes and I have it working fine when user types the content in, but when user copies text from an outside document and pastes large amount of text in, the form real-time validation slows down to such a degree as to make impression that the browser froze. On Firefox I am getting the "Script unresponsive" message and IE just looks like it is frozen. Below are the relevant portions of my form. Maybe you guys can advise what could I do to avoid this?

Relevant model sections:

<presentation-abstract 

sgrt:started-typing="false" 

sgrt:valid="" 

sgrt:show-valid="" 

sgrt:show-invalid="" 

sgrt:is-textarea="true" 

sgrt:label="Presentation Abstract" 

sgrt:error="Please enter less than 500 words" 

sgrt:hint=""/>

<xforms:bind nodeset="presentation-abstract" required="true()">

<xforms:bind nodeset="@sgrt:valid" calculate="(count(tokenize(..,' ')) &gt; 0) and (count(tokenize(..,' ')) &lt; 500)"/>

<xforms:bind nodeset="@sgrt:show-valid" relevant="../@sgrt:started-typing = 'true' and ../@sgrt:valid = 'true'"/>

<xforms:bind nodeset="@sgrt:show-invalid" relevant="../@sgrt:started-typing = 'true' and ../@sgrt:valid = 'false'"/>

</xforms:bind>

The body of the XHTML page contains this snippet:

<xforms:setvalue ref="presentation-abstract/@sgrt:started-typing" ev:event="xforms-value-changed">true</xforms:setvalue>

<xforms:output ref="presentation-abstract/@sgrt:error"/>

<xhtml:br>

  <xforms:textarea ref="presentation-abstract" incremental="true" class="input-textarea" appearance="xxforms:autosize">

    <xforms:help ref="@sgrt:hint"/>

  </xforms:textarea>

</xhtml:br>

<xforms:group ref="presentation-abstract/@sgrt:show-valid" class="valid"/>

<xforms:group ref="presentation-abstract/@sgrt:show-invalid" class="invalid">

  <xforms:output ref="../@sgrt:error"/>

</xforms:group>