When a message contains some special characters like & or < or > it is not saved correctly by the save method of sfMessageSource_XLIFF class.
Indeed the save method use createElement with the second argument as the value of the node. This way the value is not escaped correctly (see the following comment on the PHP manual page for createElement method). So either you handle the escaping by applying htmlentities to the value within the createElement method (but it is the wrong way to correct it), either you make use of the createTextNode method for the value.
I have made patches for both symfony 1.0 and symfony 1.1 branches which correct this bug, using createTextNode method.
Indeed the same bug applies to the latest RC for the symfony 1.1 branch.
Eric