This is intentional and stems from the fact that in ices, turning on crossfade will force re-encoding to activate. Some stream hosts do not use re-encoding and having it suddenly enabled would cause unexpected spikes in CPU usage.
It doesn't really apply equally on Liquidsoap (as Liquidsoap always re-encodes the audio stream) but our framework enforces the same "admin-only" limitation on these encoder settings. The global option to make these settings accessible to users can be changed in /usr/local/centovacast/etc/centovacast.conf though.
In a nutshell, definitely not a bug, but maybe not ideal either. If the demand is there we can look at pushing it up from our framework into the individual source modules where it can be access-controlled separately on a per-source basis.