SQLite select statement is not working when a column contains the '?' or the 'x' character

I noticed that whenever I try to execute an sqlite query on a column that contains strings in which the '?' (due to encoding errors) or the 'x' character is contained, the matching fails. Does anyone know why? I suspect the second case has something to do with the relative hexadecimal symbol. This holds for either sqlite version 3.7.9 and 3.8.6. Thanks in advance