NoteDelegate preview caches images even when they are removed from the note

[liufeng]

system-image-cli -i
current build number: 91
device name: arale
channel: ubuntu-touch/rc-proposed/meizu.en
last update: 2015-08-18 17:53:12
version version: 91
version ubuntu: 20150818
version device: 20150804-2287567
version custom: 20150814-887-8-46

step by step
1.Open Notes APP
2.Swipe "add note" from bottom to up .
3.Tap attachment icon to insert a picture or qr code.
4.Delete the picture or qr code and save the note.
5.Back to Notes list.
6.Tap the note to see detail.
Actual result:
After step 5, the picture or qr code still appears in the note.
After step 6, there is no picture or qr code in the note detail.
Expected result:
After step 5, the picture or qr code is not in the note.
After step 6, there is no picture or qr code in the note detail.