Saxon

After upgrading from 10.0 to 10.1, I am facing a

java.lang.RuntimeException: Internal error evaluating function ...

where the root cause is an UnsupportedOperationException with this stacktrace:

java.lang.UnsupportedOperationException
        at net.sf.saxon.value.UntypedAtomicValue.copyAsSubType(UntypedAtomicValue.java:46)
        at net.sf.saxon.type.Converter$UpCastingConverter.convert(Converter.java:188)
        at net.sf.saxon.type.Converter$UpCastingConverter.convert(Converter.java:180)
        at net.sf.saxon.expr.CastExpression.doCast(CastExpression.java:376)
        at net.sf.saxon.expr.CastExpression.evaluateItem(CastExpression.java:395)
        at net.sf.saxon.expr.CastExpression.evaluateItem(CastExpression.java:30)
        at net.sf.saxon.expr.ValueComparison.effectiveBooleanValue(ValueComparison.java:347)
        at net.sf.saxon.expr.FilterIterator$NonNumeric.matches(FilterIterator.java:177)
        at net.sf.saxon.expr.FilterIterator.getNextMatchingItem(FilterIterator.java:76)
        at net.sf.saxon.expr.FilterIterator.next(FilterIterator.java:62)
        at net.sf.saxon.tree.iter.UntypedAtomizingIterator.next(UntypedAtomizingIterator.java:44)
        at net.sf.saxon.tree.iter.UntypedAtomizingIterator.next(UntypedAtomizingIterator.java:27)
        at net.sf.saxon.om.MemoSequence$ProgressiveIterator.next(MemoSequence.java:225)
        at net.sf.saxon.expr.parser.ExpressionTool.effectiveBooleanValue(ExpressionTool.java:760)
        at net.sf.saxon.expr.Expression.effectiveBooleanValue(Expression.java:890)
        at net.sf.saxon.expr.instruct.Choose.choose(Choose.java:946)
        at net.sf.saxon.expr.instruct.Choose.iterate(Choose.java:996)
        at net.sf.saxon.expr.instruct.BlockIterator.next(BlockIterator.java:49)
        at net.sf.saxon.expr.CardinalityCheckingIterator.<init>(CardinalityCheckingIterator.java:51)
        at net.sf.saxon.expr.CardinalityChecker.iterate(CardinalityChecker.java:234)
        at net.sf.saxon.expr.LetExpression.iterate(LetExpression.java:519)
        at net.sf.saxon.value.MemoClosure.makeSequence(MemoClosure.java:86)
        at net.sf.saxon.value.MemoClosure.iterate(MemoClosure.java:80)
        at net.sf.saxon.expr.UserFunctionCall.iterate(UserFunctionCall.java:482)
        at net.sf.saxon.value.MemoClosure.makeSequence(MemoClosure.java:86)
        at net.sf.saxon.value.MemoClosure.iterate(MemoClosure.java:80)
        at net.sf.saxon.expr.VariableReference.iterate(VariableReference.java:555)
        at net.sf.saxon.expr.FirstItemExpression.evaluateItem(FirstItemExpression.java:112)
        at net.sf.saxon.expr.Expression.iterate(Expression.java:872)
        at net.sf.saxon.expr.Atomizer.iterate(Atomizer.java:359)
        at net.sf.saxon.expr.GeneralComparison.effectiveBooleanValue(GeneralComparison.java:646)
        at net.sf.saxon.expr.instruct.Choose.choose(Choose.java:946)
        at net.sf.saxon.expr.instruct.Choose.iterate(Choose.java:996)
        at net.sf.saxon.expr.LetExpression.iterate(LetExpression.java:519)
        at net.sf.saxon.expr.instruct.Choose.iterate(Choose.java:997)
        at net.sf.saxon.expr.instruct.Choose.iterate(Choose.java:997)
        at net.sf.saxon.value.MemoClosure.makeSequence(MemoClosure.java:86)
        at net.sf.saxon.value.MemoClosure.iterate(MemoClosure.java:80)
        at net.sf.saxon.expr.VariableReference.iterate(VariableReference.java:555)
        at net.sf.saxon.expr.FirstItemExpression.evaluateItem(FirstItemExpression.java:112)
        at net.sf.saxon.expr.Expression.iterate(Expression.java:872)
        at net.sf.saxon.expr.Atomizer.iterate(Atomizer.java:359)
        at net.sf.saxon.expr.GeneralComparison.effectiveBooleanValue(GeneralComparison.java:646)
        at net.sf.saxon.expr.AndExpression.effectiveBooleanValue(AndExpression.java:145)
        at net.sf.saxon.expr.AndExpression.effectiveBooleanValue(AndExpression.java:145)
        at net.sf.saxon.expr.AndExpression.effectiveBooleanValue(AndExpression.java:145)
        at net.sf.saxon.expr.AndExpression.effectiveBooleanValue(AndExpression.java:145)
        at net.sf.saxon.expr.AndExpression.effectiveBooleanValue(AndExpression.java:145)
        at net.sf.saxon.expr.AndExpression.effectiveBooleanValue(AndExpression.java:145)
        at net.sf.saxon.expr.instruct.Choose.choose(Choose.java:946)
        at net.sf.saxon.expr.instruct.Choose.iterate(Choose.java:996)
        at net.sf.saxon.expr.LetExpression.iterate(LetExpression.java:519)
        at net.sf.saxon.expr.instruct.Choose.iterate(Choose.java:997)
        at net.sf.saxon.expr.TailCallLoop.iterate(TailCallLoop.java:99)
        at net.sf.saxon.expr.parser.Evaluator$11.evaluate(Evaluator.java:290)
        at net.sf.saxon.expr.instruct.UserFunction.call(UserFunction.java:633)
        ... 231 more

Unfortunately I do not yet have a small reproduction for this, but I am working on it.