I imported an OBJ file as a Surface. I selected a section of it, went into Properties and changed the Create 3D Object As setting to Solid (there was no active option to do the same under the Format menu).
It was a reasonably complex structure, so I thought it would take a while. 3 hours later, the conversion process was reported as still active. I Escaped out of it to turn my computer off, but decided to see how many of the individual objects had been converted.
Turns out, all of them were now Solids.
The conversion process never ended on its own. I don't know how long it had been finished.
I'm using 2017, Build 28.3.
TC Pro Platinum 2018, 2017, 2016 & 2015 (all with LightWorks & RedSDK) & V21
System: i7-5820K @ 3.30GHz, ASRock X99 Extreme4, 16GB DDR4-2133 RAM, Gigabyte GTX 970, Samsung NVMe SSD 950 (256GB), Windows 7 Pro (64-bit) SP1