This was fixed previously in CONF-30255, but has reared its head again. Quoting from the original ticket:

When trying to add a Confluence page to a JIRA dashboard via the 'Confluence Page Gadget', typing the name of a Confluence space on the 'Space' field, or the name of a Confluence page on the 'Page' field returns suggestions of Confluence spaces/pages available, however, clicking on any of the suggestions does not select the suggestion to be shown on the gadget, instead, the clicked suggestion will open on Confluence. Not being possible to configure the gadget.

Steps to reproduce:

1. Add the 'Confluence Page Gadget' on a JIRA dashboard.
2. Start typing the name of an existing space/page on the corresponded field.
3. Click on any of the suggestions for the typed text.