Is the problem for you that "they influence each other"?
If so - welcome to Qlik's associative data model. Columns from different data sources brought into different tables but having the same name will associate by name. So these fields named key fields "influence" by selection and filters the records/rows from various tables accordingly.
This is not wrong - it is the brilliance of the associative data model. You can disconnect various tables if you don't want them to be associated by renaming the indentically named columns when they are turned into fields so no association it created.
Well the problem is probably not that they influence each other, but that they interact the wrong way. I want to set a filter for "Datum" (Date), so that just data is shown that involves these dates. But somehow my "cost of work" goes to zero when I set a filter, alothough there is a lot data that correspond with the filtered date.
But the idea is a good one, I will try to rename my date field for the time costs and see what happens, maybe I can find out more. Thank you!