There is white margin at the bottom of the picture when viewing in full screen

[quandan]

current build number: 206
device name: krillin
channel: ubuntu-touch/rc-proposed/bq-aquaris.en
last update: 2015-12-17 05:02:36
version version: 206
version ubuntu: 20151217
version device: 20151204-2254a36
version custom: 20151111--36-46-vivid

Steps:
1.There are some pictures in gallery
2.Open gallery and tap to view it in full screen
3.Tap the picture several times and check the bottom

Expectation:
There won't be any white margin on the picture

Actual result:
After several times hitting the picture , There is white margin at the bottom of the picture

Notes: you can refer to the attachment