The thing is:
you are adding 'AB' as SYSTEM in each row of table 2.
Since there is no sample data, I assume your Table1 does have more than 1 row. BUT you are also adding 'AB' to each row. It should look like this I guess:
... and so on
The problem is, that each row in Table2 contains SYSTEM = 'AB'. It is impossible for qlik to apply the correct mapping, because Table1 contains more than one M_STATUS for AB. So instead of mapping multiple values Qlik will automatically pick the first occurrence). As we don't know the contents of your mapping table, we can't tell you what is apllied.
P.S. If you want further advice, you should specify what you want to do, how your data looks like and add an example.
It should be not a problem for qlik. Applymap function fetches the first matched record's value even there is multiple same value on the first column of mapping table. The reason should be different.
vanderson009 If you can share a sample data, you can get more useful help from community