DNS records not being discarded when DHCP assigns IP address

This morning we received reports from our help desk that when they tried to remote control a user's PC it was bringing up the wrong computer.  We pinged a few by name and found that they all resolved to an IP assigned to another user's computer.  We did an nslookup on these PCs and verified that there is only one IP assigned to the computernames.  We checked DNS and found that there are two A records with different computernames that have the same address (one timestamp is for today, the other computer's timestamp is a week old.  The DHCP lease duration is set to 1 day). So there isn't an IP conflict going on, it just looks like the records aren't being deleted from DNS when the DHCP lease expires and the IP is assigned to a new computer. We have DNS dynamic updates enabled in DHCP and it is set to discard A and PTR records when the lease is deleted.  When we manually delete the leased IP from DCHP and the records from DNS and have the user reboot their PC, the DNS record is recreated for the correct PC and it can be remoted into.  We're just confused as to why this began happening today (we've had no issues with this previously) and why the records aren't being deleted from DNS when the lease expires.  DNS Server event log shows no errors.  

We plan on deleting all the DHCP leases and DNS records (except for our servers obviously) after all our users are gone tonight but wanted to know if there is an easier/cleaner way to do this?