Proxy DHCP failure prevents host record from saving

I'm having intermittent problems saving records on hosts which live on
subnets attached to a Foreman TFTP/DHCP proxy server. I'll make a change
to a host record (any change, such as overriding a parameter), and try to
submit the record. The form submits, but rather than taking me back to the
host detail page (ie: https://foreman/hosts/, it takes
me back to the "host" tab on the edit page (ie:
https://foreman/hosts/ No error messages are
displayed. I have to login to the foreman server, and into the proxy, to
see any errors. I'm trying to figure out what's preventing these records
from being saved.

Here's what I see in the proxy logs, /var/log/foreman-proxy/proxy.log:

E, [2016-05-16T14:36:28.157102 #19439] ERROR – : Unable to add subnet
I, [2016-05-16T14:36:28.157650 #19439] INFO – : - - [16/May/2016
14:36:28] "GET / HTTP/1.1" 400 47 0.1811

And here's what I see on the Foreman server, under

2016-05-16 14:36:28 [app] [I] Failed to save:
2016-05-16 14:36:28 [app] [I] Redirected to https:
2016-05-16 14:36:28 [app] [W] ProxyAPI operation FAILED
> ProxyAPI::ProxyException: ERF12-4395 [ProxyAPI::ProxyException]: Unable
to retrieve DHCP entry for ([RestClient::BadRequest]: 400 Bad
Request) for proxy
> /usr/share/foreman/lib/proxy_api/dhcp.rb:53:in rescue in record' > /usr/share/foreman/lib/proxy_api/dhcp.rb:43:inrecord'
> /usr/share/foreman/lib/net/dhcp/record.rb:43:in conflicts' > /usr/share/foreman/lib/net.rb:24:inconflicting?'
> /usr/share/foreman/lib/net.rb:24:in conflicting?' > /usr/share/foreman/app/models/concerns/orchestration/dhcp.rb:152:indhcp_conflict_detected?'
> /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/
_run__2668920226443293147__validation__249765768476308273__callbacks' > /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/callbacks.rb:405:in__run_callback'

_run_validation_callbacks' > /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/ active_support/callbacks.rb:81:inrun_callbacks'
run_validations!' > /opt/rh/ruby193/root/usr/share/gems/gems/activemodel-3.2.8/lib/active_model/validations.rb:194:invalid?'
> /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/
active_record/validations.rb:69:in valid?' > /usr/share/foreman/app/models/concerns/orchestration.rb:59:invalid?'

The second log seems to indicate a record conflict, and/or a failure to
retrieve the record from DHCP. My leases file contains a single
reservation for this host, and there is not a duplicate IP or MAC listed.
I also do not see a duplicate DNS record for this host. Has anyone seen
this behavior?