MYSQL - ORDER BY & LIMIT: Different result when using variable or constant

Question

Query 1:

set @userName = 'harry';

set @previousRegionId = (
        select Region as RegionID
        from log
        where User = @userName
        order by stamp desc
        limit 1);

select @previousRegionId;

Query 2:

set @previousRegionId = (
        select Region as RegionID
        from log
        where User = 'harry'
        order by stamp desc
        limit 1);

select @previousRegionId;

I expect the same result for both queries, but the result is different and it is reproduceable !

The log table contains same value in User column for all rows ('harry').

Answer 1

Changed the order by clause. Order by id works "better". Order by timestamp column is suspect ...

I am not 100% sure if this approach will work in all scenarios/aspects.