I've encountered one of these on an aircraft where the NAV/LOC/ILS and VHF Com was normally tuned by Remote Tuning Units or via the FMC. One emergency unit (gathering cob-webs) was available in case of RTU or FMC failure to directly tune both Radio-Nav and VHF Com, what you got (Nav or Com) depended upon what frequency you set.
PERHAPS the unit/s you refer to are of the same basic 'off the shelf' Collins stock, but without the Com facility. As 411A suggests, you may only be getting a nice number display without any function above 118.0