I was able to do it too but shorty there after it changes to search unless I hold down the back key.
hmm when I try to recreate on my Lumia Icon I get my open apps after long press, including Search but no Maps
Its nothing, this was also know in the prerelease of gdr3
( even the store pictogram was then replaced by music/video's pictogram ).
Its nothing else than a minor bug.
there is already a long thread about this, i forgot the title though...