Created attachment 133789 [details]
The kmy file that demonstrate it

SUMMARY
After changing the opening date of one account earlier, the consistency check fails. 
And it's quite annoying to have an error message at each save.

STEPS TO REPRODUCE
1. From an empty file, create an account with an opening balance to non zero
2. Change the opening date earlier in the passed
3. Perform an integrity check

OBSERVED RESULT
Result of the consistency check :
  * Opening date of Account 'Solde d'ouverture' cannot be changed to support transaction 'T000000000000000001' post date.
  * Transaction 'T000000000000000001' has a post date '03/12/2019' before one of the referenced account's opening date.
    Referenced accounts: Solde d'ouverture
    The post date was not updated to '01/01/2020'.

Finished: 0 problems corrected. 2 problems still present.


EXPECTED RESULT
Result of consistency check :
"Finished: data is consistent."

SOFTWARE/OS VERSIONS
Windows: Windows 10

ADDITIONAL INFORMATION
The problem come from the opening date of the opening balance account that is not updated when the opening date of some account is changed earlier. 
I manually changed the opening date in the XML file, and now the consistency check is successful.

I've also tested this issue on Linux Manjaro KDE, with the same KMyMonney version, and the result is the same.