If you enter a number using commas but no decimal points, then SSDC does not convert this to a number. For example, entering 50,000 displays 50,000 as text and if you use it in a formula, it is parsed as 50. Meaning that if A1=50,000 and B1=10, if C1=A1+B1, then C1=60 instead of 50,010.
This is an issue and we are tracking this as a defect #001659 internally.
This issue has been fixed in a recent update.