Hello,
It is a "bug" I have encountered when using v1.4.1 and is still present in v1.4.2; after 1500 comments for a single picture, it is no longer possible to view that particular picture anymore. I know that coppermine isn't intended to handle that much comments but it's probably something someone may want to be aware of.
A possible fix for this would be to allow an admin to separate the comments over more than one page.
This isn't really a bug, the comments feature is not intended to be used as a forum. However I will move this to feature requests as it would be nice to see some pagination of comments in 1.5