QTextDocumentLayout::draw() is slow if there is text selection

SOFTWARE VERSION:
libqt4 4.7.4~git20110728-0maemo7

HARDWARE VERSION:
B3.1 / XXXXXX

OPERATOR:
N/A

PRECONDITIONS:
widgetsgallery is up and running
meego-im-uiserver is up and running

STEPS LEADING TO PROBLEM:
1. select multiline text entry
2. enter about 400 characters in 20 lines
3. select 10 lines
4. try to pan application page

EXPECTED OUTCOME:
Panning should be as smooth as it is without text selection.
FPS is more than 50.

ACTUAL OUTCOME:
Panning is not smooth enough.
FPS is about 30. Difference is quite visible.

TEST CASE:
N/A

FREQUENCY OF OCCURRENCE:
always

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There is also pure Qt application available. Problem is reproducible in device and desktop.

PRECONDITIONS:
Compile test application and install to target device.
Please note that test application is pure Qt application.

STEPS LEADING TO PROBLEM:
1. Start application: ./text-test
2. FPS rate (black number inside yellow rectangle) is 49
3. Kill application
4. Start application again: ./text-test -select

EXPECTED OUTCOME:
FPS rate is the same

ACTUAL OUTCOME:
application shows 20 frames per second, so it is more than two times slower due
to text selection.