Yes, all to frequently unfortunately.
The problem is two fold, either people with learning disabilities are considered to be ineffective witnesses so the case against their abusers is dropped leaving them at risk or else they are not held to the same law as others. I think the law still struggles to accept that people with learning disabilities can be witnesses (and commit criminal acts).
The MWC report was interesting in highlighting some of these issues and caused some discussion in my workplace about situations where we have put in 24 hour care without clear legal authorisation in order to protect others because the law has been unwilling to pursue these cases in court but if the alternative is leaving children at risk of abuse what else can be done? We didn't come up with a better suggestion but acknowledged the discomfort we felt about such scenarios.