Hi,

This is indeed the first report we have on this. I'm afraid there is no way to rollback patches on Steam.

Could you send us a report.zip from our support tool? It will allow us to perhaps reproduce your problem and fix it.
It can be found here: http://www.larian.com/OriginalSinAlpha/AnalysisTool_DOS.exe
Simply run the tool and click generate report, then send this to supportdos@larian.com with a small description.

Thank you