I don't think this is a bug: it looks like 'loading complete' fires at the right time, so as long as you switch to another layout or stop updating the progress bar it should work correctly. The reason it goes down again is because the 'loadingprogress' expression has a second purpose: to reflect the loading progress when the game is downloading an update in the background (see offline games in Construct 2 for more info). The game is ready to run as soon as 'Is loading complete' fires, since it is fully downloaded, but offline caching (writing content to disk) takes longer and happens in the background while the game is still running. So in fact I believe it's working correctly.
The game should not block when going to other layouts after 'is loading complete' first fires. If you still have a problem with that, please submit another .capx that demonstrates the issue.