Thanks again, dandarc if only for confirming that I am not insane and this is legitimately strange.
I spoke with the HR department a while ago and reviewed my original W4 on file and there is nothing in the additional withholding box.
MDM, thanks for all the data.
Payroll functions at my company are handled by the dreaded ADP. Due to a glitch, they weren't taking out medical and dental for a few paychecks when they should have. Now I'm covering those double for my next few paychecks. I have a good handle on my cashflow, so I can manage that, but I've noticed that the second time they're charging me for medical and dental doesn't have the fine print that says it's pretax.
Obviously, that's disconcerting, but it shouldn't make such a huge difference, should it?
Also, any idea on if I should contact ADP directly versus my own HR department?
dandarc, thanks very much for the weekly/bi-weekly point. I think you may have hit the nail on the head here. My position is maintenance translator, so my department is in the plant, where they're paid weekly, but I spend most of my time in the office, where we're paid bi-weekly. I'm betting they changed my pay to bi-weekly, but not my withholding. I will confirm with HR and post the results here.
Again, many thanks to everyone!