Created attachment 116043 [details]
Screenshot how it looks in 4.4
In Impress 4.4 and earlier, going to View -> Master (in the main menu), one sees a sub-menu with two radiobuttons - Slides master and Notes master.
Selecting Slides master, a toolbox (or whatever that is) pop-up appears near the top edge of the slide, enabling to exit the master view. See the attached screenshot.
In Impress 5.0 this is no longer the case. Firstly, there is no radio button next to slides master submenu (but an icon). Secondly (and more annoyingly), the toolbox no longer appears and it is impossible to get out of the master view back into normal view ... or maybe it is possible, but I didn't figure out how.
Created attachment 116044 [details]
Screenshot how it looks in 5.0
There's no toolbox appearing really (it's not just that I forgot to include it in the screenshot :))
This might however be platform and desktop-environment specific, so one might not be able to reproduce on other platforms.
I'm on Linux (Fedora 21) and use KDE
I'm bumping severity a bit, it's really annoying that one can't get out of the master view
+ this is a regression, it used to work in 4.4
Toolbar is still there, just now docked by default.