Setup: dual master (probably not relevant), N slaves, everything MariaDB 10.0.10
All servers essentially the same config (copies from same source with only server specifics changed)
Binlog format MIXED
InnoDB engine
Parallel replication enabled
All charset settings utf8

Table/column utf8.

utf8 string inserted on active master, reads back ok.
On other master (acting as slave), incorrect (charset mangling)
On some slaves, OK
On other slaves, incorrect

Which slaves get a string incorrect changes per row, so it's not always the same ones.

Interesting isn't it?

Verified by doing SELECT SHA1() on the affect column, to rule out any client mangling.

SELECT string, SHA1(string) FROM t\G

Correct:

string: Atlético Madrid
SHA1(string): 6dec52f694515702664a20b7660574139267a46a

Incorrect:

string: Atlético Madrid
SHA1(string): db4bb2aa6aae25ce19e0dda3626d37fa356c673e