avoid trying to modify frozen tag object
avoid trying to modify frozen tag object

fixes #1380

1ec5/iD,zbycz/iD,openstreetmap/iD,kartta-labs/iD,ngageoint/hootenanny-ui,AndreasHae/iD,energiekollektiv/openmod.sh-id,1ec5/iD,mapmeld/iD,morray/iD,mapmeld/iD,kartta-labs/iD,morray/iD,ngageoint/hootenanny-ui,bagage/iD,openstreetmap/iD,1ec5/iD,bagage/iD,edpop/iD,tbicr/iD,andreic-telenav/iD,ngageoint/hootenanny-ui,edpop/iD,kepta/iD,andreic-telenav/iD,kepta/iD,mapmeld/iD,openstreetmap/iD,tbicr/iD,AndreasHae/iD,edpop/iD,digidem/iD,digidem/iD,AndreasHae/iD,kartta-labs/iD,energiekollektiv/openmod.sh-id,zbycz/iD,bagage/iD