I’ve had a look and calling .SelectDistinct() isn’t going to work because the .Select(fields) from the custom fields list overrides it, it would need to call .SelectDistinct(fields) which I’ve just added to OrmLite.
I’ve also added support for DISTINCT in AutoQuery in this commit by prefixing your fields list with DISTINCT, e.g:
/query?Fields=DISTICT Field1,Field2
This change is available from v5.0.1 that’s now available on MyGet.