Search comments field for CIs (device)

One of our users have discovered some sort of a bug or issue that I was not aware of. It seems when you do a CI search and use an advanced find on the comments field using "contains" it never turns up any results. This works with other fields but not with the comments field. Is this because of the type of field that comments is?

Also, I noticed text search has a visible condition of [$has.ir.key]. Can someone explain to me what this means and why it's not visible with the device table/CI search?