Replacing thumbnail doesn't change thumbnailImage_thumb version

[and]

Replacing an auto-generated thumbnail doesn't change all the versions Plumi generates.

Eg. this is the original  http://www.engagemedia.org/Members/cpa/videos/manduku/thumbnailImage_thumb This is the image it should be replaced with  http://www.engagemedia.org/Members/cpa/videos/manduku/thumbnailImage

The thumbnailImage_thumb version is the one that appears in the listings.

[and]

Dimo rightly points out that this is a caching issue but it can take a day or more to get it to change (even if you force refresh). One work around is to take the thumbnail later into the video (resulting in less need to replace the thumbnail) but is there another work around to do a harder refresh on the thumbnail?

[and]

Talked with Dimo - he going to look at varnish caching setting in Engagemedia specifically as atm Plumi comes with the default Plone settings and we don't want to change this.