I just noticed...
Code:
_talon.configPeakOutputVoltage(+12.0f, 0.0f);
... which caps the output to forward only. If you want to spin reverse you should do...
Code:
_talon.configPeakOutputVoltage(+12.0f, -12.0f);
... which allows full motor output in both directions.
I think the peak outputs get reset to the defaults when you save in web-config.