Problems combining 2 Tables

[MiKeZZa]

Hi guys,

I'm having problems combining 2 fact tables and a DAX-measure. Can you please help me to understand what we're doing wrong?

This is our datamodel:

And when we're making a combination of a field in a fact table and a summation of another field from another fact table it's ok:

But when we don't want to sum the field but make a DAX-calculation for it something goes wrong:

We really can't understand this. The DAX-formula is shown in this printscreen; as you can see it sums the uitbetaaldefte field, just like our first printscreen, but it divides it by something from the date dim. But this gives a strang multiplication of data; the person that had 1 'arbeidsrelatie' in first printscreen now has all the available 'arbeidsrelatie' choices plotted to it; this is not correct...

We think it happens because of combining 2 fact tables, but we also do this in printscreen 1 and there it gives no problem, so it is caused by our DAX-calculation. But even when we change the DAX to this the multiplication comes:

Aantalftes_Uitbetaald = 
            SUM ('edm uitbetaaldefte'[uitbetaaldefte])

But this DAX must be the same as the normal SUM.....

So we are really desperate... What are we understanding/doing wrong?

Our datamodel is: