ID 480149 - Annotations: Undo/Redo doesn't work

Problem summary
Ctrl/cmd+Z doesn't work for annotations.

Customer reported version
Flix 6.3.5

Steps to reproduce
1) Open an existing sequence revision and click on the annotation tool for any panel.

2) Draw something on the panel, then draw something again.

3) Hit Ctrl/cmd+Z on the keyboard.

Expected behaviour
Second drawing to be undone, the first one to stay.

Actual behaviour
Nothing happened.

Reproduced by support
This bug has been reproduced in:
6.3.6 - macOS 10.14 Client - Windows 10 Client
6.1.2 - macOS 10.14 Client - Windows 10 Client

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