PE will remove VLAN tag and forward "pure data" on the other side, so that's correct that you don't see any VLAN tag. ( you can even have different VLANs on both sides and it will be working ). The symmetric means that you will pop/push same VLAN ( if I remember well )
It's better to you use pop ( even with double tagging ) because you will save 4/8 bytes which is not much but why you should transmit those bytes if it's not necessary
Have a look at this troubleshooting technote, it might explain what you're experiencing. As stated, by default pseudowires are established in ethernet mode (type 5) and does not require to transport VLAN tags. VLAN mode (type 4) will transport VLAN tags.
However, just having done this on an ASR9000 using sub-interfaces (type 5) without rewrites it seems that the VLAN ID is transported across the pseudowire. Using type 4 the dummy vlan (id 0) is appended to the frame.
I seem to recall something about the catalyst 7600 doing it differently. I believe that they popped the VLAN by default and pushed then on egress when using sub-interfaces and type 5 pseudowires. So it may be platform-specific what you're experiencing.