While the next version doesn’t fix this bug I propose an different solution. But I like it so much that I will use it forever:
1. With Automator create (or copy and past from link bellow) an applescript to open a new tab in finder (from the last opened folder):
https://gist.github.com/n8henrie/0ceef75964bd153f910d
2. Before the last line of AppleScript ("end run”) copy and paste this line to set the sidebar width:
tell application "Finder"
to set the sidebar width
of every Finder window to 180
3. Run and test the script and set the sidebar witdh (180) to the best value for you.
4. Use OSX AppleScript Editor to Export this script to an “Add New Tab.app”. A good tip is export and save it to the folder that you want to be the default tab folder (in the case when no tab was already opened).
http://www.engadget.com/2008/01/13/applescript-saving-scripts/
5. After export and save it, move “Add New Tab.app” to Applications folder.
6. This app is going to use some Accessibility features, so is necessary add it to the list "System Preferences-->Security and Privacy->Privacy->Accessibility” and authorize it to control the computer.
https://support.apple.com/en-us/HT202802
7. Now we need only create an keyboard shortcut (Shift+Command+T) in Finder to run “Add New Tab.app” to open a new window (if no window already opened) or tab. After this we can use it in place of default shortcut (Command+T) to open new window or tab with correct width (see the tutorial bellow):
http://computers.tutsplus.com/tutorials/how-to-launch-any-app-with-a-keyboard-shortcut--mac-31463
ps: A good tip is to set this shortcut in all applications and not only in Finder to open a new finder window when necessary. You have to make some small additional steps:
8. Go to System Preferences -> Keyboard -> Application Shortcuts -> All Applications
9. Add new line with properties:
Application: All Applications
Menu Title: New Tab
Keyboard Shortcut: Shift-Command-T
10. Now, test the shortcut. This Service will appear at every app into Services menu and will work as you want.