secret lengths of OnBehalfReason

As I was setting up a custom SharePoint workflow to work with an external user outside of the domain, I noticed some quirky behavior and error messaging from SharePoint.

e.g. it works if its a short piece of text like the MOSS 2007 SDK:

createPartnerReviewTask_TaskProperties1.OnBehalfEmail = "null@void.com";
createPartnerReviewTask_TaskProperties1.OnBehalfReason = "This user does not have access to this Windows SharePoint Server site.";


but dies like this when its too long:
WinWF Internal Error, terminating workflow Id# 7c4d...
System.ArgumentException: Value does not fall within the expected range.
at Microsoft.SharePoint.Workflow.SPWorkflowTaskProperties.set_OnBehalfReason(String value)

what range is specified in the reference? undocumented.