Bachelor Winner Has It With Relationship Rehab

Vienna and boyfriend Kasey Kahl were hammering out their issues on the show -- but during a routine sit-down, sources close to production tell us, producers blindsided her ... bringing out Vienna's previous ex ... Lee Smith.

In case you don't remember -- Lee is the guy Vienna was allegedly sending flirty emails to while she was still engaged to "Bachelor" winner Jake Pavelka.

According to sources, Vienna had an emotional breakdown and walked off the show -- screaming at producers that she "hates" them. She hasn't been back since and the show has finished shooting.