Description:
Apparently, Writer doesn't track changes in formulas. So, if I edit a formula, and when hit "Undo" button, it will undo previous operations (Like creation of formula object, or any other normal change), but not the changes that happened inside a formula.

Steps to Reproduce:
1. Create a formula
2. Make some arbitrary change (for example, write something)
3. Edit a formula
4. Hit Ctrl+Z (or undo button)

Actual Results:
Arbitrary change (step 2) gets undone, then creation of formula itself

Expected Results:
Changes to formula (step 3) get undone, then the arbitrary change, then the creation of formula itself


Reproducible: Always


User Profile Reset: Yes


OpenGL enabled: Yes

Additional Info:
Version: 6.4.2.2
Build ID: 1:6.4.2-0ubuntu3
CPU threads: 4; OS: Linux 5.4; UI render: default; VCL: gtk3; 
Locale: en-US (en_US.UTF-8); UI-Language: en-US
Calc: CL