Show stacking and show history timestamp

Beginning with software release 15.18, the 2920 switch displays the show stacking command twice and an entry with a blank space after entering the show history timestamp command. For example:

switch# show history timestamp
3 Wed July 25 2015 07:00:51 show stacking
2 Wed July 25 2015 07:59:31 show stacking
1 Wed July 25 2015 07:59:35
switch#

Note that this is expected behavior.