UserAgent: Mozilla/5.0 (X11; CrOS x86_64 10682.0.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3431.0 Safari/537.36
Platform: 10682.0.0 (Official Build) dev-channel samus

Steps to reproduce the problem:
1. open 5 tabs and pin them
2. open a bunch more tabs so there are at least 3 that get 'stacked' on top of each others
3. close one of the unpinned tabs. noticed how the unpinned tabs redistribute themselves across the entire window width, occluding the pinned tabs.

What is the expected behavior?
The pinned tabs should not be occluded by the unpinned tabs.

What went wrong?
The pinned tabs were occluded by the unpinned tabs.

Did this work before? Yes it worked back in 2018 May, at least.

Chrome version: 68.0.3431.0  Channel: n/a
OS Version: 10682.0.0
Flash Version: 30.0.0.85 /opt/google/chrome/pepper/libpepflashplayer.so

I noticed this issue back in May or June, when I was asked to switch to the dev channel to confirm that another bug had been fixed. The dev channel had a build with the regression. It was the first build with the 'stacked' tabs feature.