This comes down to how you have encoded your receipts.

More than likely, you are using the [[S120:dc:donorName]] to pull in the name for the receipt.  Transactions are stored to the transaction table as snapshots of the transaction at the time that they were made.  So that S120 tag is pulling the name of the Donor at the time that the transaction was made.

If you have Receipt Manager enabled, you can edit your custom receipt.  You may want to use the S1 tag with something like this:

[[S1:FIRST_NAME]] [[S1:LAST_NAME]]