I have noticed a bug in the Opportunity Quick Create functionality where it does not work as you would expect when enabled. Here are the steps to reproduce:
1. Enable Quick Create for the Opportunity Product entity
2. Create a new Quick Create Form for the Opportunity Product
3. On the Opportunity entity, add a subgrid for the Opportunity Products with a custom view (I don't use the 'opportunity product in line edit view' since i can't add custom fields)
4. publish all customisations
5. Navigate to an opportunity and click the '+' sign on the new subgrid to add an opportunity product. At this point CRM navigates to the full New Opportunity Product record form instead of the Quick Create form. However, for example, when you add a new Contact to an Account, the Contact Quick Create form loads up (assuming it is enabled).

Furthermore, the Opportunity Product entity does not have a field lookup to the Opportunity (there is a relationship but no field) which renders the Quick Create functionality for the Opportunity Product useless.

Please fix this asap.
Thanks