Updated Cover doesn't transfer to Ereader

Hello

Brand new user of Calibre.. a tremendous resource I am still figuring out.
I have a Kobo Glo (CDN eh), some books when transferred to the reader
were missing covers. These are Epubs, no DRM. So deleted them from the
reader, updated the metadate and made a cover was there and tried again
with no luck?

When I check with the viewer option, I also do not see a cover.
I then discovered the Epub modify plug-in. By using that and the cover
update option, both the Viewer (under Win 7,IE) and when downloaded
to the Ereader work. So I have a work around but it
seems like an extra several steps when if the update/change metadata
worked as I think it should, then the plug-in should not necessary, at least for
correcting metadata/covers!

Then again, maybe I'm doing something incorrectly and if so, point me in the
right direction but my searching of past issues is what let me to the plug-in.

Many thanks.