Theme change loses comments

Hi Gang,
Working on a new site, and have a single page with comments right now. If I use a default theme, or one installed with the Install Themes tab, everything is fine.
However, there are two themes I downloaded – Animals3 & Pets Theme – which make the comments disappear.
If I activate another theme, the comments are there. Then when I switch activation to either of the manually installed ones, the comments are gone.

Suggestions?

Thanks!