Dialog/Modal with dynamic widths

[trueleader]

On a DetailsList an user gets ~50 relevant entities to interact.
If he click on one of it, a Modal is opened containing the details of the entity which he may edit.
This fields are grouped in a Pivot with ~8 PivotItems. Most of the PivotItems contain relative small content (label+input). One PivotItem contains a DetailsList with related files. Another one contains one more DetailsList with ~8 columns / ~50 rows with sub-entities (user can add, delete, sort, open details, ... on them) ... some of the columns have fixed size, some have unknown content size which should be visible in a single line as much as possible.

As of the nature of the mixed PivotItem content, the dialog should change its width on demand.
I added a minWidth to ensure the change between PivotItems will not be to extreme.

The maxWidth I set seems not to work in combination with the rendering of the included DetailsList: On my 4k display max used rendering width seems to be < 50%: https://codepen.io/NE-Maxworx/pen/ExozJma

May this be a bug? Or is this a problem with dialog vs table widths (dialog waits for content size and table waits for size of dialog)?
Any other suggestions?