Looks as if the Brazilians have been having VERY similar problems
snip
The cookie jar
The Senate staff and the company contracted to build, deploy and maintain the Senate's electronic voting system, gave their word that such leakage was not possible, since the system was "100% secure". Meanwhile, a political foe of that Senate president was elected to succeed him, in a fierce political battle. The new Senate president then ordered the premises sealed and a serious audit. An university team (Unicamp) did the audit job, under a lot of pressure, and a public investigation by the legislative power was set up.
This audit and public investigation exposed an electronic voting system (that of the Senate, made to order for the Senate as specified by the Senate) rigged with built-in backdoors and vulnerabilities, allowing, for example, the system operator to vote, before the day was over, for senators not present during voting sessions, through the infamous "botão macetoso".
image 3: photo by Joedson Alves/AE from the senate session of June 28, 2000
It turned out that this system, according to Unicamp's audit, allowed for 18 different ways to leak the list of individual votes in secret ballotings. A trail of traces of leakage of the votes on removal of the junior senator was also found. This leakage employed the most cumbersome and convoluted of those 18 ways: recompiling to set up yet another backdoor in the application, running, reverting after. This trail pointed to the system operator.
and more...
http://www.brunazo.eng.br/voto-e/PIcontest/PI2003contest-act1.htm.