Apparent problem with divert-to rule parsing

While porting a 4.9 pf.conf to 5.2 I came across something that looks  
like it might be a bug. The affected line was the pass in rule to send  
forward FTP requests to the proxy on the firewall.

The following rule would not load:

pass in quick on $IntIf inet proto tcp to port ftp divert-to lo0 port 8021

The error message was:

pf.conf:207: address family mismatch for divert

If lo0 is replaced with 127.0.0.1 then it loads and works correctly.  
However, 127.0.0.1 is properly substituted for lo0 when using rdr-to.

George