Courtesy time signatures/keys do not disappear if courtesy measure is moved
1) Place time signature/key so that courtesy appears on next system
2) Add/remove adjacent bar so that courtesy measure moves to different system
3) Note that the courtesy signature/key creates a double with the real signature/key
The easiest way to work around this is to disable show courtesy in the inspector yet in Musescore 2 courtesy's would automatically disappear when not needed.