This bug is preventing the use of Slic3r from MatterControl interface (at least on deltas). I ran into the same issue.

There seems to be a bug report #773 already opened for this, but no one yet assigned to fix.

Hopefully this gets fixed as I really like the MatterControl interface.

I usually prefer the MatterSlice as well, but sometimes it would be nice to compare quickly and easily.

Not sure how those high values could have gotten in there, but I'm glad you have it worked out now.