The current RegExFilter class uses a ByteArrayBackedCharSequence to set the data to match against. The ByteArrayBackedCharSequence contains a line of code that prevents the matcher from properly matching multi-byte characters.
Line 49 of ByteArrayBackedCharSequence.java is:
return (char) (0xff & data[offset + index]);
This incorrectly casts a single byte from the byte array to a char, which is 2 bytes in Java. This prevents the RegExFilter from properly performing Regular Expressions on multi-byte character encoded values.
A patch for the RegExFilter.java file has been created and will be submitted.