Since this commit: 4616eb0 , the function PMA_getSpecialCharsAndBackupFieldForExistingRow (in libraries/insert_edit.lib.php) contains this code:
} elseif ((substr($column['True_Type'], 0, 9) == 'timestamp' || $column['True_Type'] == 'datetime' || $column['True_Type'] == 'time') && (strpos ($current_row[$column['Field']],"." ) === TRUE) ) {
As you can see, the last condition is: strpos([…]) === true.
This shouldn't be possible… strpos will return a number or false.
I think that this condition will never be true.
Fixed with https://github.com/phpmyadmin/phpmyadmin/commit/65f360b33f05a837fe4068768f23c4e28dbb8f1a