Sandy,

It takes off the extension and splits what's left into tokens with delimiters space, _, or -. Then it checks those tokens against a fixed list of matches. For T1's the current list is 

{'MT1','ST1','T1','MPRAGE'}

I agree that T1w should be added, especially since it's the BIDS standard as you pointed out. For the next version I'll add some various "w" and "-w" suffixes, and check over the BIDS list to add anything else too.

Thanks for bringing this to my attention. I've generally considered the "automatic" to be a bit "at your own risk", but BIDS types should definitely be made to work.

0.3.4 is coming very soon, so this is good timing to get it in there.

Chris