Hey Tiger! Thanks for reporting — I noticed that the other day but didn’t have time to dig in. It should be fixed now, I just tested it. Let me know if it still doesn’t work.
As for extra space, if the geotiff before had no tiles or overviews I believe the overhead is somewhere in 20–30%. But many people put those in already, since it tends to make the images perform better on most systems, even desktop GIS. So if you’ve already got some sort of pyramid/overview and/or tiling it won’t introduce much additional space.