Unexpected scrollbar in Reporting Services

Question

I try to display reporting service report in iframe, and i have a interesting issue. Sometimes, but not always, there is some extra horizontal scrollbar. Solution have to work only in IE 9, 10, 11. I could not find any rule, why it happens.
Problem dissapears, when i hide header of report using rc:Toolbar=false. It occurs only in iframe.

Reporting Services 2008 R2

Answer 1

There is a very simple solution. Issue occurs because parent document has html doctype and it is rendered by current IE engine. Default Reporting Services template has line like:

<meta http-equiv="X-UA-Compatible" content="IE=5">

I found information, that IE cannot render document inside iframe using different engine.

I deleted this line and changed doctype to "html". Problem disappeared