Unable to run subscrition using sao

Steps to reproduce:

1. Open the web client (sao)
2. Create a subscription service and a monthly recurrence.
3. Create a new subscription, set the start date in the future. For example the first of the next month.
4. Add a line to the subscription. Check the start date is the same as the one set on the subscription line.
5. Click quote button to save the subscription. Everything works well until here.
6. Click the Run button to run the subscription.

Current behaviour:

The following error message is shown: Pre-validation - The values of "Lines" are not valid.

Expected behaviour:

It is possible to run a line in the future.

I reproduced it on the 6.8 demo database. Everything works well using tryton.