In cubase 8.0.40, if you are doing multitrack editing using the folder group edit function, have lanes collapsed and an event in the folder selected, then use the slice tool on the selected event, the slice will be applied to all of the takes on the track you click upon - BUT - on the other tracks in the folder, the slice will only apply to the selected take.
You can see it in this screengrab - I made 3 splits to a selected take 4, with lanes not showing; the first split near bar 1.2 (mouse clicking on track 1); the 2nd split at 1.3 (mouse clicking on track 2); and a 3rd split just before 1.4 (mouse clicking on track 3). When lanes are shown, it looks like this:
I would assume and expect that, because group editing is on, whatever I do to one track would be replicated on the other tracks in the folder.
This leaves one in the messy situation where takes underneath the selected take might go out of sync in subsequent edits, as group editing no longer applies to them.
Would someone mind testing this in 8.5, please? 
When I posted this in the issues subforum, it was rejected as off topic - maybe it’s been fixed? Or maybe I’m not understanding how the behaviour is intended to work 
Here’s the repro:
Group editing loses sync if an audio event is selected and the split tool is used on it.
- 1. Create empty project.
2. Add 3 audio tracks.
3. Move the tracks to a folder and enable group editing.
4. Set left and right locators 1 bar apart, enable cycle mode in the transport.
5. Arm “record-enable” on the 3 tracks.
6. Hit record button, record 4 passes, stopping 4th take before it gets to the right locator. The 4th take events will be selected and a darker colour than the 3rd take:
7. Change to the “split” scissor tool.
8. Make sure “snap to zero” is off. While take 4 is selected, make a left mouse click split on track 1 “audio 01”, make another split on track 2, and a 3rd split on track 3:
9. Show lanes on the 3 audio tracks. Takes 1-3 are now out of sync. A split is made across all takes only on the track which received the mouse click. Toggling group editing brings up the “group editing could fail” warning:
Aside from the failure to transfer edits to all grouped events, there’s a secondary issue of what the correct behaviour of the split tool should be - ie: should only the top selected take be split, or should all the takes be split? To me, it’s better if only the top selected take is split, as I’d rather keep the takes underneath intact. We have the comp tool for making splits across all takes.