I have a combo with custom template inside the form. On the same page i have vault and richtext editor.
Here is a screenshot of how the combo is rendered on the page.
If i override this css declaration it seems to fix it.
Unfortunately I was not able to reproduce your issue locally.
The following snippet seems to work well:
Please, makes sure that you are using the latest version builds of all the using dhx components.
If the problem still occurs for you please, provide a complete demo, where the problem can be reconstructed.