ID 472583 - Dialogue: No record of empty dialogue histories for panels

Problem summary

Should dialogue be removed from a panel, there is no way to easily track when this was done and by who, because the dialogue history pane doesn't show empty dialogue entries between other dialogue changes.

Customer reported version
Flix 6.3.5

Customer reported platform
macOS 10.13

Steps to reproduce

1) Add a panel to a clean sequence revision, add dialogue on it, then save the revision.

2) Delete the dialogue from the panel, then save the revision.

3) Now add a different dialogue to the panel, and save the revision once more.

4) Check the dialogue history dropdown.

Expected behaviour
Three dialogue histories should be displayed. One for the first saved dialogue entry, one for the dialogue being removed, and one for the second dialogue entry.
Should a sequence revision be saved against a panel before dialogue was added to it, that first empty dialogue that was saved against that panel shouldn't be logged because the use of the dialogue history is to track down changes made to the dialogue.

Actual behaviour
Only two dialogue histories are displayed.

Reproduced by support

This bug has been reproduced in:
6.3.6-2 - macOS 10.14 Client - CentOS 7 Server 

6.3.4 - macOS 10.14 Client - CentOS 7 Server 

6.1.2 - macOS 10.14 Client - CentOS 7 Server 

Earliest version tested
6.1.2 - This issue appears to be in all versions of the product