QDomDocument setContent() performance downgrade from 5.1.1 to 5.3.1

When a XML file has lots of entities, 5.3.1's XDomDocument.setContent() take long time. 5.1.1 performs well.

<?xml version="2.0" encoding="utf-8"?>
<!DOCTYPE math [
<!ENTITY angzarr "⍼">
<!ENTITY cirmid "⫯">
<!ENTITY cudarrl "⤸">
<!ENTITY cudarrr "⤵">
<!ENTITY cularr "↶">
]><mn>10</mn>

The example's number of entities is too small. You have to make it above one thousand. Then it will take one or two seconds to finish.
I will attach a file.