Quite strange though, I can use the normal characters without encoding them. I know its best practice to encode so but still strange that this doesn't work for thavorac.

maybe it works without encoding in some cases. I tried once to use in odoo domain statement in XML a & symbol as AND operator, it doesn't worked, then reverted back to encoded version: & amp ; and it started working. since I'm using only encoded versions of these 5 characters, to be sure...

Guess I'll always use encoding from now on then!

You may need to use < instead of <

A similar expression for other special characters.