lupdate does not encode the values in the id attribute

When using qsTrId in qml file, the lupdate will take the value as is and put it in the id= attribute without encoding it.
This results in a .ts file that is invalid, when the value contains invalid XML characters, like an &.
Running lupdate a second time will give an error on the file lupdate itself created.

Example QML file:

import QtQuick 2.0

Text {
     //% "This text will fail in lupdate"
     text: qsTrId("this&that_will_fail")
}

run lupdate creates a file containing:

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE TS>
<TS version="2.1">
<context>
    <name></name>
    <message id="this&that_will_fail">
        <location filename="test.qml" line="5"/>
        <source>This text will fail in lupdate</source>
        <translation type="unfinished"></translation>
    </message>
</context>
</TS>

Running lupdate againon the with the same ts file will result in the following error:

lupdate . -ts languagestrings.ts
Scanning directory '.'...
Parse error at languagestrings.ts:6:37: Expected ';', but got '"'.

I would not expect lupdate to ever generate invalid output files.
I could not find any restrictions on the characters that are allowed to be used in the qsTrId.