I think you may be on to something mgelb.
I removed the 6 additional themes from the wp-content/themes folder and only left the Default and Classic that come with WP, went back into the ADMIN Dashboard, clicked Appearance and then Themes. This is what the page looks like:
Then I downloaded Pixeled.1.5 Theme from WP, unzipped and copied the Pixeled folder to the wp-content/themes folder. This time when going to the ADMIN Dashboard and clicking on Appearance/Themes I now see an additional Theme available. However, there also appear to be an error. The error says:
The following themes are installed but incomplete. Themes must have a stylesheet and a template.
Stylesheet is missing.
See the image here,
The interesting thing I think is that it does not say what theme is broken or incomplete. Per the image I posted yesterday when all 6 of the additional templates were installed I got the same message. It also did not say what theme(s) was broken or incomplete.
See image here,
When checking the available Themes on WordPress this morning I noticed that some of the ones that I pulled down yesterday are no longer there.