VLAN on (open) vpn tunnel interface

Hi list,
In my setup several VLANs go through one VPN tunnel. This works
flawless as long I have no service like DHCP or HTTP server running on
one of the VPN-VLAN interfaces.

works:

client connector		LINUX VLAN Bridge	Client Nets

client2a-vlan2--\		/tap0.2--bridge--eth2|---|client2b
	 	 tap0|=====|tap0
client3a-vlan3--/		\tap0.3--bridge--eth3|---|client3b

works not:
client2a-vlan2--\		/tap0.2--DHCPD/HTTPD
		 tap0|=====|tap0

client3a-vlan3--/		\tap0.3--bridge--eth3|---|client3b

With tcpdump I see the VLAN tagged DHCP replies leaving tap0 of the
Server/Bridge but listening on tap0 of the client connector
shows only untagged packets.

Is this a known issue or do I have to (re)^n check my setup?

Sorry, if this is the wrong list (as introduction of VPN causes the
trouble) I'll move to openvpn but I think here exists more VLAN related
knowledge.

Best
 Christian