If I get paid biweekly, but missed a pay period, so get a check for four weeks instead, should not my net simply be double what I normally get for 2 weeks? They increased my tax deductions, so that my pay is less than what it normally would be if I divide the 4 week check in half. I worked the same number of hours every week.
Your reasoning is sound, and you are correct. What most likely happened is that they withheld as if you earned all that within one pay period. That could be someone on the payroll end not doing the calculation correctly, or not knowing how to override the default pay-period calculation, or an inflexible payroll software that doesn't allow for exceptions like that.