On my TDAmeritrade account, I am getting transactions labeled MANDATORY - NAME CHANGE. There is a transfer in for the total number of shares, and then a transfer out for the same number of shares. In both cases, all prices and dollar amounts are zero. There isn't a change in the ticker symbol. The result is my basis is cut in half. The transfer in is always before the transfer out.
Deleting these transactions resolves the problem and going forward I will skip importing them. I doubt there is a anything FM can do to mitigate this (I can easily visualize how this is coded and it is certainly an unexpected edge case that would have to look at multiple transactions to resolve). I guess this is more of a heads up to other users.