strange "lag" and cpu usage when previewing certain HTML mail in KMail

[O. Sinclair]

On Kubuntu 14.04 I have noticed that certain HTML mail take several 
seconds before preview (or open). During the "lag" KMail basically 
freeze and my laptop fan runs amok. CPU hits 25% KMail on a i5 second 
gen Intel w 4 Gb RAM

It is difficult to give examples as it is not all HTML but one is 
basically any from cnet.com (I subscribe to several newsletters).

Has anyone else noticed this or is it unique to something in my 
setup/configuration.

This is KDEPIM 4.13 with the baloo indexing

Kind regards
Sinclair