I have just upgraded our site to Umbraco version 4.6.1. Everything looks like its working but if I use the preview button the whole site/backend slows down since umbraco uses a lot CPU for each request in preview mode.

Here is a snippet of the trace output  from the preview mode:

aspx.page Begin PreRender 0.313144547700895 0.000023 
aspx.page End PreRender 68.8758778001115 68.562733 
aspx.page Begin PreRenderComplete 68.8759356286902 0.000058 
aspx.page End PreRenderComplete 68.8759607715506 0.000025 
aspx.page Begin SaveState 68.87818535596 0.002225 
aspx.page End SaveState 68.8792234767268 0.001038 
aspx.page Begin SaveStateComplete 68.8792514132383 0.000028 
aspx.page End SaveStateComplete 68.879491667237 0.000240 
aspx.page Begin Render 68.879515972002 0.000024 
Runtime Engine Umbraco is running in preview mode. 69.2981616378618 0.418641

And here is the same trace output when not in preview mode:

aspx.page Begin PreRender 0.00745094697789803 0.000033 
aspx.page End PreRender 0.327630187635579 0.320179 
aspx.page Begin PreRenderComplete 0.327688016214351 0.000058 
aspx.page End PreRenderComplete 0.327713159074687 0.000025 
aspx.page Begin SaveState 0.329501375174778 0.001788 
aspx.page End SaveState 0.329919026021464 0.000418 
aspx.page Begin SaveStateComplete 0.329945845072488 0.000027 
aspx.page End SaveStateComplete 0.329970149837479 0.000024 
aspx.page Begin Render 0.329993337142011 0.000023 
aspx.page End Render 

Has anyone seen this behaviour before? I have no idea how to solve the issue?