2008R2 DC owning PDC FSMO role does not become Domain Master Browser
See edits of question.
Wins still has different number of entries, but seems to function well. So I'm closing this.
The problem with the interval of the master browser events is fixed to. We got rid of them alltogether. Problem was the DHCP helper of the cisco routers. The did not only forward dhcp and bootp but also a lot of other protocolls in the default config. See http://www.cisco.com/en/US/docs/ios/12_3/ipaddr/command/reference/ip1_i1g.html#wp1108053 for details.