This build, (1703), released on 5th October, 2013, is the first update to 2.50.x after the release of 2.50.0 Final on 21st December, 2012.
It is primarily a bugifx release, but it also introduced some UI improvements for ZQuest, and a few minor features.
The ZScript API specification did not change.
The internal version ID increased from 24 (2.50.0) to 29 (for 2.50.1).