[Form Block] Date picker shows blank field if multiple form blocks have it

### Quick summary

Reported in: 6188710-zd-woothemes

If multiple form blocks have been added with a date picker, the other form blocks will not display the date until the other forms have been submitted.

### Steps to reproduce

1. Create a new page or post.
2. Add a Form Block to the page/post.
3. Either choose the "Appointment Form" option or manually add the date picker to the form block.
4. Add a second Form Block to the page/post and choose the "Appointment Form" option.
5. Publish the page/post and view it on the front-end.
6. Attempt to change the date for the first Form Block, then the second Form Block.
7. Notice that changing the date in the second Form Block will also change the date in the first Form Block, but the second Form Block will display a blank date field.

### What you expected to happen

For the dates to display in both form blocks and to be completely separate. Changing the date in Form B should not impact Form A

### What actually happened

Changing the date in the second form block changed the date in the first form block. The second Form block also shows the date field as blank.

### Impact

Most (> 50%)

### Available workarounds?

No but the platform is still usable

### Platform (Simple and/or Atomic)

Simple, Atomic

### Logs or notes

Reproduced on the Twenty-Fourteen Theme and Adventurer theme on both Simple and AT sites.

Reproduce the issue on a published page with two Form Blocks using date pickers, as described in the steps. No source file or test is named; trace the date-picker behavior between both blocks and consider the work complete when each field displays and changes its own date independently.

Written by the indexing model from the issue text.