@nyalldawson @borysiasty removing this breaks tab behaviour: it does not show the right tabs anymore now :-(

@nyalldawson @borysiasty currently you cannot see the plugin manager settings...

And I'm not able to use the 'install from zip' here on a windows machine today's master.
I downloaded the plugin zip:
http://plugins.qgis.org/plugins/pdokservicesplugin/version/0.14/download/
or (experimental should be enabled):
http://plugins.qgis.org/plugins/pdoklocator/version/0.1/download/

All seems fine, but after clicking the 'Install plugin' nothing happens, no apparent install, and no error?

OR is it related to this tabs being wrong?

@rduivenvoorde - yes, removing the spacer item changed the tab numbers, so you just need to click "Settings" in order to get the "Install from zip" :) And "Settings" are currently not available.

@nyalldawson - what do you propose instead of the spacer? Let's discuss it in qgis/qgis3_UIX_discussion#24