Mail shifting up after viewing HTML email

Mail shifting up after viewing HTML email

Hi, I have a strange problem.  I use Google Chrome for Zoho Mail (this doesn't happen with Internet Explorer).  When I read an HTML email the whole web page shifts up about 30 pixels.  I've attached a screenshot showing an example.  This happens every time I open an HTML email.  Any idea what could be causing this?  I'm using the latest version of Chrome.

Thanks.