[CMS] Replacement variables not being applied to CMS?

[nforums]

I've optimized my images folders to be served from subdomains to have parallel downloads which has greatly increased my page speed, but the CMS has the domain name prefixed to forum paths which caused a minor snag. (<img src="{vb:raw vboptions.bburl}/)

To get around this I want to use the replacement manager

For "Search for text" I have entered

<img src="{vb:raw vboptions.bburl}/

For replace with I have entered

<img src="

Theoritically that should remove the {vb:raw vboptions.bburl}/ from the templates correct? But it doesn't seem to be affecting them at all, and the images remain broken. If I manually edit the templates to remove that then all is well.