I was recording an audio track when all of a sudden something strange happened to my midi tracks. They sounded out of sync. I noticed in my midi piano track that the midi clip had a dim grey look to it, similar to when you mute a clip, but it wasn't being muted.
 
I then found a strange shape event in the midi event list at 0.000. I deleted that event and the midi clips returned to their normal look and were fine. When they were dim also I couldn't copy and paste a bar, it was like the whole midi track was locked from any changes like overwriting or copy and paste.
 
Any clues what this feature is? It looks similar to mute clips or clip gain, but it affected all clips in the track.

Sounds like the Edit Filter was set to edit MIDI automation of some sort. Deleting the Shape event would remove the envelope and switch the Edit Filter back to Clips. 

Yeah, what Brundlefly said. The "dim" effect is simply the automation layer being drawn on top of the midi layer. You can't edit the midi layer because you can't select it through the automation layer. To fix this, you can just click on the little button in the corner of the track info that if you hover over it says: "Automation Lanes = OFF". This will toggle it to "Automation Lanes = ON" and will move that layer to it's own lane so you can edit your midi again. :)

This is very strange. I'm not using a simple instrument track, I'm using the old midi track method of a midi source and an audio source. In this case I have 2 midi tracks one is my 1st scratch track and it's muted and 2nd one was my final midi track and that's the one that's dimmed. If I look at the audio source track it's set to clips and that was one of the first things I checked when this happened. Just in case I just changed clips to automation volume and then back to clips -  no change.
 
I'm including a picture of the 2 midi source tracks and the audio source track. The bad midi track is on top and clearly looks dimmed. I think it is some strange sort of envelope, because in the dimmed state I can't copy and paste one bar in the staff view. Or even select all the clips in the bad midi track and copy to a new track.
 
I've had this same thing with the dimmed midi track happen on 2 different songs. It just happened suddenly. I’m not sure what I did to cause it.  I just shift clicked on the bad midi track and it returned back to a normal view. The shape disappeared from the event view also. This should indicate it is some sort of envelope. . But what? Is this a bug?
 

it appears to me at least, you've been playing with colors (editing them in preferences)
you some how changed the track color background (for track with focus).
 
in other words, when a clip is selected it is in focus.
try looking at your focus color in preferences / customization/ colors.
 
you probably mistook it for Track View background. as that looks to be the same color as your tracks.

chuckebaby
it appears to me at least, you've been playing with colors (editing them in preferences)
you some how changed the track color background (for track with focus).
 
in other words, when a clip is selected it is in focus.
try looking at your focus color in preferences / customization/ colors.
 
you probably mistook it for Track View background. as that looks to be the same color as your tracks.

I went back to the Mercury theme and haven't made any color changes. That still doesn't explain why the 2 midi tracks look different - one is dim and acting strange.

What happens if you click on the "Take Lanes = OFF" button? Could be that you pasted some midi notes and they were added, again, as a take layer on top of your other track? (I do this constantly)

Boscoe
What happens if you click on the "Take Lanes = OFF" button? Could be that you pasted some midi notes and they were added, again, as a take layer on top of your other track? (I do this constantly)

 
I turned the take lanes on and at the top is the normal looking clip and below it are the dim clips. When I turn take lanes off again it returns to the dim clips in the track - so this has no effect.
 
I'm beginning to think this is a bug or if something in my setup has become corrupt. I've never seen this before, except in these 2 songs that I started from my custom normal template on the same day. For now I've reverted to an earlier image file, since things seem unstable. I'm still using 2016.05 and this is the first time this is come up.
 
The fact that I can Shift click on the clip and get it to return to normal seems to indicate that this is one of the envelope modes like automation, but it still shows edit filter=clips, instead of automation. And I see no envelope line in the clip as you can see in the picture.

This probably doesn't make any difference but in your screenshot, you have Write Automation enabled.

Bristol_Jonesey
This probably doesn't make any difference but in your screenshot, you have Write Automation enabled.

 
True, even in my template I have write automation enabled. It's always enabled. It's not enabled on any individual tracks until I get ready to do a final mix and then I only automate volume one track at a time, not everything. If I need to automate anything else which is very rare I individually enable that parameter.