Using "mender-artifact cp" to modify image results in unwanted naming changes

mender-artifact cp hosts raspberrypi3_release_1_1.6.0b1-build1.mender:/etc/hosts

--- /home/kristian/Downloads/before	2018-08-02 15:32:40.222262778 +0200
+++ /home/kristian/Downloads/after	2018-08-02 15:32:50.610055514 +0200
@@ -1,16 +1,16 @@
 Mender artifact:
-  Name: release-1_1.6.0b1-build1
+  Name: raspberrypi3_release_1_1.6.0b1-build1.mender
   Format: mender
   Version: 2
   Signature: no signature
   Compatible devices: '[raspberrypi3]'
   State scripts:
 
 Updates:
     0:
     Type:   rootfs-image
     Files:
-      name:     core-image-full-cmdline-raspberrypi3.ext4
+      name:     mender-artifact232213585
       size:     218103808
-      modified: 2018-08-01 18:29:56 +0200 CEST
-      checksum: 4e11b5d656316829f3155cad864ac493cb592608eedd621965c4d6447d41cfa0
+      modified: 2018-08-02 15:27:42 +0200 CEST
+      checksum: fba88b3cad40f86e6484e721f9c12f9211fc57c8fb67ae23befd06795a8d83d4