Raidz1 with 4 disks, only 3 disk activity lights

Hi, just a quick general question which has bugged me for years.

I know that for raidz1, an odd number of disks is recommended. However, there’s nothing stopping you from running raidz1 with an even number of disks. I have had multiple servers running raidz1 with 4 mechanical HDDs because I needed the space and 1 disk fault tolerance is fine with me. I get the “power on” light on all 4 disks, but only 3 “disk activity” lights. The dashboard tells me that all 4 drives are in use. Since it’s unlikely that all my servers have exactly one activity light broken, I was wondering if this is expected behaviour or if the dashboard is lying to me.

That was before compression;

As for the activity LED, I don’t know.