Using Asterisk 1.4.26.1 + DAHDI 2.2.0.2, the FXS lines on my TDM840B get their FSK VMWI spill as expected. Testing * 1.6.1.5, same DAHDI, results in no FSK spill, only a line polarity reversal.
Stutter dialtone is correctly generated in both cases.
Is anybody running a similar setup with FSK MWI devices? Does it work for you?