When the line of pinned posts comes to an end, a pinned post title gets line broken if there is a space in the title. If there is no space in the title, then the previous title with a space gets line broken.
pin1 pin2word1 SPACE pin2word2 pin3word1 SPACE pin3word2 pin4word1 SPACE LINEBREAK
pin4word2 pin5word1 SPACE pin5word2
In this way a title gets split between one word on line 1 and one word on line 2. It confuses me, and I think readers would be confused as well.
To me it would make more sense to linebreak not in the title of a pinned post, but between titles of different pinned posts, like:
pin1 pin2word1 SPACE pin2word2 pin3word1 SPACE pin3word2 pin4word1 SPACE pin4word2 LINEBREAK
pin5word1 SPACE pin5word2
Maybe a cosmetic bug to be fixed?
The only solution I found so far to not linebreak in the middle of a post title is to replace the space with a character or symbol and add a space at the end of each pinned post title. I ended up using ˜ instead of a space between post title words, just to avoid the linebreaking in inopportune places.
A workaround, which does not work under every circumstance I found, is to use either of:
markdown:   (nobreak space character)
said to be legacy:   (nobreak space character)
Old blog post titles (from 2 years ago) seem to not take this into account. New blog post titles do.