Possible Render Speed related Bug ?

Hello,

I created some filters for my personal work and in doing so, I noticed a possible Render / Speed bug when processing the same source image:

Filter #1 consists primarily of blend components linked together with switches and offsets. By itself, this filter generally takes about 3-5' to render an image.

Filter #2 consists of an edge component plus some blend, channel and switch components. By itself, this filter generally takes about 30' to render an image.

Filter #3 consists of all the components from Filter #1 followed by the components of Filter #2. This combined filter requires more than 10 hours to render.

Can somebody shed some light on this?

Thank you, jeremy