I have all the latest Gallery Assits modules as of today.
I deleted an image from a gallery and it as deleted from this folder: "files\gallery_assist\1\gallery_assist189\img". But the 2 imagecache files were not deleted from these 2 folders:
1. files\imagecache\gallery_assist-gallery_assist-thumbnail-100\gallery_assist\1\gallery_assist189
2. files\imagecache\gallery_assist-gallery_assist-preview-550\gallery_assist\1\gallery_assist189

I ran cron, deleted all sites cache and the images are still there.