Created attachment 155442 [details] after changing 12 to 11 date format crashed Having a date filed formatted as YYYY.MM.DD. Editing only accepts YYYY-MM-DD format. If I enter the date in YYYY.MM.DD. the cell value is converted to text. In the sample attached, I changed 2018.12.01. by replacing 12 to 11 and the cell stopped working as a date cell. I had to enter the full date as 2018-11-01 .
Thank you for reporting the bug. Please check your "Date acceptance patterns" in Menu Tools/Options.../Language Settings/Languages. Maybe you need to add the pattern "YYYY.MM.DD" for your locale. And please attach a sample document, as this makes it easier for us to verify the bug. (Please note that the attachment will be public, remove any sensitive information before attaching it. See https://wiki.documentfoundation.org/QA/FAQ#How_can_I_eliminate_confidential_data_from_a_sample_document.3F for help on how to do so.) I have set the bug's status to 'NEEDINFO'. Please change it back to 'UNCONFIRMED' once the requested document is provided.
Created attachment 155448 [details] sample spreadsheet demonstrating the error I have created a sample spreadsheet with the current state that shows the error. I will check the settings right away.
Created attachment 155449 [details] input mask change fixed the problem After adding Y.M.D. to the accepted date formats in Language->Languages the input problem is fixed. However I don't know think it is fortunate that we need to set the input mask in a quite hidden setting instead of accepting the current display format.
Ok, closing.