P: Export using Percentage results in wrong dimensions under certain repeatable scenarios

This issue is on Lightroom Classic 7.4.   If you export using Width&Height, Long Edge, Short Edge or Dimensions with no number in the size value fields and then do an export using Percentage than the percentage value is ignored.  If correct values are in the above 4 dialogs than the Percentage export will work correctly.  The dialogs for Width&Height, Long Edge, Short Edge or Dimensions should not allow an export if the length fields are not filled in with valid values.  The problem does not seem to correct itself unless you do an export with a valid value is the above four export choices.  

See this U2U thread for more detailed explanations and examples.  https://forums.adobe.com/thread/2508201