This issue has been closed as 'Won't Fix' due to an extended period of time without updates. If this issue is important to you please let us know by posting on the AnswerHub or UDN, and Epic will re-open the ticket for further review.
I'm seeing multiple issues when trying to edit a vector track.
1. A lot of the time it wont even let you add a key with shift click.
2: If you have a certain channel open, and you right click to add a key to that channel, it will want to add the key to a different channel, one that is not even visible. IT should respect the visibility of the tracks. Say you have 2 tracks visible, X and Y, it should give you 4 options when you right click, add key to X, add key to Y, and key to X and Y, and add key to all tracks.
It seems like this issue might be that when you right click, it is detecting hidden curves and wanting to keyframe them.
3: If you have 2 tracks visible and shift click one of them, it will sometime keyframe the wrong one, even though they are not close to each other.
Edit Addition: Added link to AnswerHub post where user is experiencing an issue where he can still see the 'Add Key to X' only. I have attached screenshots for reference.
Tested this in 4.8.3 for comparison.
1. In any project, Add a new Timeline to an Event Graph.
2. Create a new Vector Track
3. Hide and Lock the X and Y curves.
4. Right click on the remaining visible curve (Z).
Expected: It will only allow you to add a key to the visible and unlocked curve.
Outcome: Only shows the 'Add Key to X' curve.
Head over to the existing Questions & Answers thread and let us know what's up.