An album that contains nothing but grouped images still appears in the Album tree.
If the picture count is turned on, it reports (accurately) the number of images in the folder, but when the album is selected, no thumbnails appear (appropriately since, they have been grouped with pictures elsewhere).  This is confusing/misleading because the album tree shows an folder with a certain number of images in it, but when selected is empty. It's also a little annoying because it clutters up the album tree with useless albums.

In my case, there are hundreds of these folders; after transitioning from Picasa, I grouped the files in the ".picasaoriginals" folders with their current versions.

Reproducible: Always

Steps to Reproduce:
1. Create an album (A1) with a version of an image in it.
2. Group the image in A1 with an image in another album.
3. A1 still appears in the album tree, and (if turned on) shows that it contains 1 image

Actual Results:  
Select A1 and no images appear

Expected Results:  
"Group" to me, intuitively means that multiple files are to be treated as one image as far as digiKam is concerned.  Consequently I would expect the album counts to reflect that, and when the album count is (effectively) zero, to suppress display of the album. Or at least, I would like to have a toggle for that behaviour.

I otherwise, quite like the grouping behaviour; it's very useful. It might be handy to have the option --- in addition to the toggle to collapse/expand grouped images beside the primary one --- to toggle groups displays entirely (i.e. be able to turn them off so the secondary images reappear in their actual albums, and, in turn, the albums reappear in the tree view).