Diebold, which at some point renamed themselves Premier Election Solutions, has admitted that voting machines used in 34 states contained a software bug that caused the machines to drop votes:

The GEMS system is supposed to save information from one card at a time to be counted in order as the cards are read by a database that Riggall described as the “mother ship.” But a logic error in the program can cause incoming votes to essentially shove aside other votes that are waiting in the electronic line before they are counted.

Diebold’s stance is that the error should have been caught by election officials, so long as they followed proper procedures and double-checked that the reported number of memory cards counted matched the expected number from the precincts.