text{field,edit} with long text content take noticably longer to add typed character

A simple textEdit element when filled with a lot of text (1000s of characters) takes noticably longer to visually insert a typed character than when filled with little text.
It is expected that it should always take roughly the same amount of time to display text and the time is dependent on how much of the text is visible.
Attached is a simple qml file with a single TextEdit element that has a single (extremely) long line of text.
Run it in qmlviewer, and hit a key. Notice that it takes a second or two to update.
If you have xresponse installed, you can time it using :

> xresponse -w 5 -k 'X' | grep '864x480+0+0'

eg:
with only 100 characters in textEdit.text :
> xresponse -w 5 -k 'X' | grep '864x480+0+0'
6195173ms : 13ms : Got damage event 864x480+0+0 from 0xe2 (SCREEN)
with ~2.5million characters in textEdit.text :
> xresponse -w 5 -k 'X' | grep '864x480+0+0'
6345243ms : 1243ms : Got damage event 864x480+0+0 from 0xe2 (SCREEN)

ie, 13ms vs 1243ms

NB#221739

It is quite noticeable if you reproduce this by hand (as it was reported to us) - ie enter a lot of text, ctrl-a, ctrl-c, ctrl-v - rince and repeat - then attempt to type a character; at some point, it is very sluggish.