Unpredictable sorting of integers with QSortFilterProxyModel

I've been using a table model with a sort/filter model in PySide6 and ran into a problem where integers are sorted incorrectly, and somewhat unpredictably.

It looks like the sorting problem occurs on the C++ side, in the following function:

...
bool QAbstractItemModelPrivate::isVariantLessThan(const QVariant &left, const QVariant &right,
...
    switch (left.userType()) {
    case QMetaType::Int:
        return left.toInt() < right.toInt();
    case QMetaType::UInt:
        return left.toUInt() < right.toUInt();
    case QMetaType::LongLong:
        return left.toLongLong() < right.toLongLong();
    case QMetaType::ULongLong:
        return left.toULongLong() < right.toULongLong();
...

Adding some print debugging to the Python side, it first looked like an obvious case of everything being compared as signed 32-bit integers:

 left: 690636980    0x292a48b4   c_int(690636980)  c_long(690636980)
right: 2885968800    0xac0463a0   c_int(-1408998496)  c_long(2885968800)
l < r: False

left: 15471165    0xec123d   c_int(15471165)  c_long(15471165)
right: 2346638763    0x8bdeddab   c_int(-1948328533)  c_long(2346638763)
l < r: False

However, as I mentioned the sorting being unpredictable, other values seemed to be compared correctly:

 left: 2754875217    0xa4340f51   c_int(-1540092079)  c_long(2754875217)
right: 1983291963    0x7636a23b   c_int(1983291963)  c_long(1983291963)
l < r: False

left: 2346638763    0x8bdeddab   c_int(-1948328533)  c_long(2346638763)
right: 11220746    0xab370a   c_int(11220746)  c_long(11220746)
l < r: False

Looking back at the C++ code, I realized the switch only checks "left.userType()", so the issue seems to be that when the left value is small enough to fit into a signed 32-bit integer, the larger value accidentally gets converted to one as well.

I haven't used Qt in C++ and don't know how QVariants behave there, but I'm guessing you'll be more aware of your integer types and there's no implicit conversion like this, so I'm reporting this as a PySide/Shiboken bug.

I've attached a small example which should demonstrate the issue in a table view. I commented out the print statements (lines 44-53) since the output is somewhat verbose, but they're there just in case.

I originally spotted the issue with PySide 6.3.1 and confirmed it with 6.3.2. I also downgraded to 6.2.0 and the same thing occurs, so it doesn't seem to be a recent regression.

I realize there's an easy workaround by just doing your own sorting in lessThan() and avoiding the C++ calls altogether, but it feels like a "gotcha" for integers which aren't anywhere near breaking 64-bit limits.