I've written a grok filter that leverages the thorn character. þ. When you start logstash you get the following error and messages don't flow through the system.
The error reported is: \n invalid byte sequence in US-ASCII"}
If i replace it with another character, the same messages flow through perfectly.
For sure it is fixed under 1.4.x but you must be sure that your config file is UTF-8 encoded to be parsed correctly
Following PR propose a more helpful check and message