Description:
I just downloaded version 6.2.5.2 (x64).  I use Calc to track my supply of medications.  This includes when I can order refills.  I have the date fields formatted as mm/dd/yy.  However, upon entering a new date, the field changes to ###, because Calc changed the format to mm/dd/yyyy.  

If I change the format back, it reverts whenever I enter new data.  

If a date value is entered in an empty field, the default format is still mm/dd/yy.  Then, when a another entry is made in that field, it is automatically changed to mm/dd/yyyy.  

Steps to Reproduce:
1. Enter a date value into a non-date field, and it acts as expected. 
2. Enter a date value into a field formatted as mm/dd/yy. 
3. Calc changes format to mm/dd/yyyy. 
4. Example:  change 04/18/19 to 7/29. 

Actual Results:
07/29/2019

Expected Results:
07/29/19


Reproducible: Always


User Profile Reset: Yes


OpenGL enabled: Yes

Additional Info:
[Information automatically included from LibreOffice]
Locale: en-US
Module: SpreadsheetDocument
[Information guessed from browser]
OS: Windows (All)
OS is 64bit: no 

Renderer: Intel(R) HD Graphics 3000
Vendor: Intel
Memory: 2108 MB
Version: 3.1.0 - Build 9.17.10.4229
Shading language version: 1.40 - Intel Build 9.17.10.4229