cadaver: Prompt not working properly

I'm experiencing a weird issue with cadaver: the promt is somehow broken, i.e. it's not shown, until another output is triggered. Here is an example (and how to reproduce it):

marco@mdickert:~$ docker run --rm -ti alpine:edge
/ # apk add cadaver
fetch http://dl-cdn.alpinelinux.org/alpine/edge/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/edge/community/x86_64/APKINDEX.tar.gz
(1/4) Installing ca-certificates (20191127-r0)
(2/4) Installing expat (2.2.9-r1)
(3/4) Installing neon (0.30.2-r6)
(4/4) Installing cadaver (0.23.3-r4)
Executing busybox-1.31.1-r8.trigger
Executing ca-certificates-20191127-r0.trigger
OK: 7 MiB in 18 packages
/ # cadaver https://cloud.pinknet.de/remote.php/webdav
Authentication required for misterunknown on server `cloud.pinknet.de':
admin
Password: 
Username: help
dav:/remote.php/webdav/> Available commands: 
 ls         cd         pwd        put        get        mget       mput       
 edit       less       mkcol      cat        delete     rmcol      copy       
 move       lock       unlock     discover   steal      showlocks  version    
 checkin    checkout   uncheckout history    label      propnames  chexec     
 propget    propdel    propset    search     set        open       close      
 echo       quit       unset      lcd        lls        lpwd       logout     
 help       describe   about      
Aliases: rm=delete, mkdir=mkcol, mv=move, cp=copy, more=less, quit=exit=bye
version
dav:/remote.php/webdav/> The `version' command requires 1 argument:
  verrsion resource : Place given resource under version control
^Cdav:/remote.php/webdav/> Terminated by signal 2.
Connection to `cloud.pinknet.de' closed.
/ #

As you can see, the first line after "Authentication required" is my username, but the prompt "Username: " is not shown until I entered my password and pressed enter.

Same with the help command: it triggeres the correct output inklusive the prompt, but only after I hit enter.