Hate to be a broken record but is this happening to anybody else.  I enter a new PO, I enter a due date for a part, I tab through to the promise date and enter the same date and when I hit enter the due date changes and I have to go back and re-enter the due date again.  This happens almost every PO I enter or edit.
 

Which version of PO-A?  T6 or T7 (or BK)?

hmmmm.......  Go to System Manager - TAS-G ; Highlight the username (access code) you are using; click Edit User; highlight Mfg; highlight PO: click on Menu Lines; on the left side screen look at "&A - Enter Purchase Orders" line and tell us what the entry is under program name.
 
Make sure to click on Close and Exit for TAS-G

Did a check in both EVO and Classic views of T7POA and did not observe the behavior stated above - ours seems to work the way you would expect.

Yeah - well, perhaps Colin or Lynn can let you know if there is a setting somewhere that makes it behave like that?

Ahh! - important info - if it happened all the time, then perhaps it might be an esoteric setting, but if it is intermittent, that is unlikely.