pg_restore -t table doesn't restore PKEY

I have dump of an entire database and I'm trying to restore only one named table:

> pg_restore  --format=c -C -U myUser -d myDB /tmp/mydump -t my_table

The command completes without errors/warnings but the resulting table in the database is missing the PKEY constraint !

Is this done on purpose ? What is the correct way to restore a named table ? 

I know I can use the -t switch during the dump and then restore without using -t but I would like to avoid this solution. The files I can work on are dumps of the entire DB.

Thanks for your help,

Jan