Logstash 5.0.0-alpha2 - Can't update plugins

I'm trying to update plugins to resolve an existing problem with 5.0.0-alpha2, but getting two different issues:

Updating a specific plugin with bin/logstash-plugin update logstash-output-rabbitmq responds with

Update is not supported for manually defined plugins or local .gem plugin installations, skipping`

Trying to update all plugins with bin/logstash-plugin update asks me to confirm a bunch of plugins, and then fails after confirming logstash-filter-fingerprint with

ERROR: Updated Aborted, message: undefined method `version' for nil:NilClass

So it appears that I'm not able to update any plugins at all. Is this known behaviour?