Perhaps interesting for other Dude users:
Since about 12 hours The Dude was telling me that my DNS servers where randomly failing. This was strange, because they seemed to work just fine in practice. I checked again, dug a little deeper and found out that the DNS probe works (by default) by making a DNS request on the mikrotik.com domain. In turns out that Mikrotik is having a problem with there DNS server… At least I get very bad response when requesting that domain from a multitude of DNS servers in The Netherlands.
Mirkotik: are you experiencing some problems with the DNS server that hosts mikrotik.com?
I now changed the DNS probe to query for google.com and it cleared all the false DNS error reports The Dude was sending me.