Testfor SelectedItem Bug

When I put the following command into a command_block :
testfor @a[team=P1] {SelectedItem:{id:skull}}
and I run it while I'm in team 1 and have a skeletton skull selected it gives no signal. It says "Zuzu_Typ did not match the required data structure".
But when I cahnge the command to
testfor @a[team=P1] {SelectedItem:{id:minecraft:skull}}
^^^^^^^^^^^^
It works.