there is a miscalculation happening when you're nearing midnight (e.g. 23:59:59.999999), but not quite there yet (e.g. the decimal part of the julian date rounds to the next day), jdcal will round to the next day, but openpyxl would apply the full decimal part, adding 23:59:59.99999.
This fix neutralizes openpyxl when jdcal has already done the "jump"
Please edit the PR to be based on 2.2. FWIW Excel only has 15 digits of precision.
well, to be honest, it was as fix for 2.1.4, but I think it can go straight in 2.2, people interested in the actual hotfix can use my fork.
Now we're on 2.2 I'd only do a 2.1.6 release for security reasons.