Why are titles sometimes placed in the middle of a newspaper article?
Perhaps Chinese press is just more flexible in this particular respect. I searched and found the following from a book:

标题可以插在文字中间,也可以对角设置,或放在文尾,或分散在文中等。但是，要注意标题与文章不能分离或错位。为了使标题既能突出又能活跃版面，在同一版面中应为不同的稿件设置标题的多种排列形式。

Another article says:

Ⅰ 直题：报纸版面以直题为主。
Ⅱ 横题：用以调节版面，通常至于四角，不宜横于版面中央
Ⅲ 叠字题：可分直题横排和横题直排。
Ⅳ 横直题：横直运用，即是运用眉题。
Ⅴ 对角题：新闻集锦或花絮的标题，多方右上角及左下角。
Ⅵ 包中题：标题放在文章中央，可避免顶题及调节版面均衡。
Ⅶ 分题：新闻内容长，非一个标题所能概括时，需要分题。
Ⅷ 插题：即小标题。

It seems that titles can be put in a variety of places. They can even be put at the end of articles. People also try to apply different styles for titles on the same page, in order to avoid repetition, boost readability and get more balanced typography.
In particular 包中题 is given as the name for titles in the middle of articles. However, I searched and could not find much reference for this term, so I don't know how popular the term is.