In some of the designer templates, the post titles will have a different appearance in post pages, when compared to the post titles in the homepage. Often, the title's font is smaller and has plain font color. In some templates, the font is completely different.
Why is it so? Well, it is made that way. Nothing is wrong with it. But you can make the post titles in post pages look like the ones in the homepage, easily.
That will be all folks. Hope you guys are finding the new Blogger UI shiny and useful. If you need help with anything, use the contact form to get in touch with me. Cheers and God bless.