The function: Max(AsNumber(VALUE)) should return an error in the event that VALUE is not a number. Instead this function will return a null value. This bug can cause expressions that should have returned an error to return null instead.
Another expression that this bug can be seen is in the BuildDate function. BuildDate is often used to create a date from 2 or more fields in a database. In the event that an invalid date is stuck into BuildDate it will return a null if it is used as a parameter of another function (like DateDiff).
The most common expression that this error will occur in, are type casts (AsNumber, AsString, AsDate). These functions can take a variety of data types, and will not be able to rely on the type checking that databases have built in.