It is not an error, it's a documented limitation that has been around for many years. The 15-digit resolution limit is part of the Excel specifications, which XOR suggested you read. See:
https://support.office.com/en-us/art...7-269d656771c3 - returned by inputting 'Excel specifications, Calculation specifications and limits' into a web search. It also explains why the format suggested by gebobs won't work.