I have "Open new tab next to current tab" in my Settings, and prefer things that way, especially since I tend to have a lot of open tabs.
I experimentally tried pinning a few of my always-open tabs (eg, Gmail) this morning. Which is fine, but now all of my new tabs are opening at the right-hand end of my tab bar (way off the screen, so it scrolls the tab bar furiously), instead of next to the pinned tabs at the left-hand end, where they belong.
When you open a new tab from a pinned tab, it should open as close as possible to the pinned one -- that is, in-between the pinned tabs and the unpinned ones.
0.99.128.2.1-beta (WebKit 619.1.11.111.2)
Sonoma (14)