Extend is missing the update tab and the install new module button

The Update Manager Module is activated but the Extend UI looks like the following ( tried in B16 and the Dev version ):

https://dl.dropboxusercontent.com/u/8578/b16.png

while on beta 15 it looks like the following:

https://dl.dropboxusercontent.com/u/8578/b15.png

admin/reports/updates is showing the update tab as well as the "install new module or theme" button for both b15 as well as b16 and the dev version.

https://dl.dropboxusercontent.com/u/8578/b16%20available%20updates.png

b16 as well as the dev version were clean installs out of the box. I've voiced the issue yesterday on irc and the guy i talked with told it sounded odd and i should better report it to the issue tracker.

My setup:
MAMP 3.4 on OSX 10.10. using Apache 2.2.29, php 5.5.26 and mysql 5.5.42. The PHP OPcache is deactivated cuz i am using codekit for local development.

The steps (tried with b16 and the dev version - both fresh installs):

• I've created a db and user.
• Copied the drupal folder into my mamp htdocs folder.
• Started the install.
• Chose english as language
• The only warning the status report brought up on install is that the OPcache is deactivated - i've clicked "continue anyway"
• After linking the db, installing all the modules and creating a user i went to the extend menu point
• There i've activated (installed) the update manager module.
• As already shown above the update tab as well as the install new module button is missing: https://dl.dropboxusercontent.com/u/8578/b16.png
• I've also tried to deactivate (uninstall) the module and reactivate (install) it afterwards. But nothing changed. :/

If you need any further informations let me know. Best regards r.