Here is the situation: Some time back you developed a Schedule Table Style that references one or more Property Set Definitions and it has served you well and been used in many drawings. But now you have decided that you need to add a new property to one of those Property Set Definitions, and add a new column to your Schedule Table Style to display the values of that property. You diligently edit the Property Set Definition and Schedule Table Style in your office's central source file and test it out in some newly created drawings and all is working well.
You then announce the change to the rest of the firm, and someone who has a project in progress tries to add the new Schedule Table Style to an existing drawing that already had the old version. No matter how many times the new Schedule Table Style is dragged into the existing drawing in Style Manager, it seems as though the old version refuses to leave. Worse yet, if you delete all existing instances of that Schedule Table Style from the drawing and purge the old definition, when you add the new one, is still does not have your newly added column! What gives - is your drawing doomed to being eternally haunted by the old version of the Schedule Table Style?
Fortunately, the answer is no. The reason why the new Schedule Table Style loses the new column is that the old Property Set Definition is still present in the existing file. When you imported the new style into a new drawing to test it, it would have brought along the new version of the Property Set Definition, provided it was not defined in the new drawing (which is why you should keep your styles in source files and import them when needed, and not preload them into your template files). But, if the target file already has a Property Set Definition of that name, which would be the case in that existing file that had the old version of the schedule, the new Property Set Definition is not imported and the old version will remain. And since the new property does not exist in old Property Set Definition, the column referencing that property gets deleted from the Schedule Table Style.
The solution is to copy the new Property Set Definition into the existing file first, then copy the new Schedule Table Style. Now the new column will stay in the Schedule Table Style, and you are good to go. Of course, if the new property is a manual one, any existing objects/styles will have the default value, which you will likely need to edit, unless the default value just happens to be correct.