helm: helm del --purge bash: flaghash[${flagname}]: bad array subscript

I’m using helm on MacOS 10.13.3:

15:38 $ helm version
Client: &version.Version{SemVer:"v2.3.0", 
GitCommit:"2342275b61e0539d259590975cfb78f23afcc1e3", GitTreeState:"clean"} 
Server: &version.Version{SemVer:"v2.3.0", 
GitCommit:"d83c245fc324117885ed83afc90ac74afed271b4", GitTreeState:"clean"}

If I type:

helm del --purge

followed by tab, I get:

bash: flaghash[${flagname}]: bad array subscript

This seems to only occur with the --purge flag, it does not occur otherwise.