If a plugin adds it's own page to an existing menu section (say, for example, to the Goals plugin), the menu will not be selected when the plugin's page is loaded. This is because Piwik will only activate/highlight the Goals plugin section if the module is
'Goals', but since the page is added by another plugin, the module will be different.
The menu JS should use another mechanism to figure out which menu section is currently active.
FYI: For reporting menu it already works differently in
Is it necessary to fix it in 2.15 if it's already changed in 3.0 then?
It is necessary if @mattab still thinks it is required to fix the problem affecting a new plugin. Probably a good idea either way for the LTS version.
I think it would be nice to fix if it is easy, ie. can be done in less
than 1h. Otherwise Imho it will be OK to wait for 3.0 where this is