We have the same here, seems the default 2017 install settings are set to inventor files for some silly reason? How can you change it?
In SolidWorks 2017 with 3DInterconnect we can now import native 3rd party files into SolidWorks assemblies as below.
Mine defaults to SOLIDWORKS files though so my thinking is that it remembers the last used selection?
I inserted an IPT and then went back to the command and it defaulted to this, then swapped to a SW file and then afterwards it reverted back to SW files.