Comes from this CQF pass through test.
Querying for a number less than decimal 0.3 should return the double 0.3, because a double 0.3 is actually 0.2999999999999999888. So,

t.insert({y: 0.3})t.find({y: {$lt: NumberDecimal('0.3')}})

Should return

{y: 0.3}

This is not a type bracketing issue.