I think that I am also experiencing this problem. Have you found a solution?
I've tried to use the Salesforce connector a few times and each time run into limitations that pushed me back to using the Excel data extractor tool, which is quite a limited solution itself. I don't have to work with Salesforce anymore, but if I did I would look at warehousing the data locally. Aside from the limitations and idiosyncrasies of the connector, one of which you mentioned, the lack of ability to transform the data before bringing it into Tableau is a big problem in itself since Salesforce tables are big and flat so you're limited to fairly simple reports.