Switching from asynchronous to synchronous context causes some bucket methods to hang

The following asynchronous methods never complete when called from a synchronous context:
IBucket.ExistsAsync()
IBucket.QueryAsync() with a query containing StartKey and EndKey

Example:
bool Exists(string id)

{ return bucket.ExistsAsync(id).ConfigureAwait(false).GetAwaiter().GetResult(); }

The symptom does not occur when run from unit tests, but happens with 100% regularity inside an ASP.NET WebApi service. No exceptions are thrown, the task just never returns.