[...] in the function _STLReader_::check_stl_type() (STLReader.cc file) you assume that a STL is  encoded in ASCII format by looking for the keyword solid, i.e., line 476:

   //check for ascii keyword solid
   if(strnicmp("solid",&line[firstChar],5) == 0)
   {
     return STLA;
   }

The problem is that also some binary STL files start with the "solid" keyword, and it seems the standard allows it, at least looking at the first references I've found:

https://people.sc.fsu.edu/~jburkardt/data/stla/stla.html
https://people.sc.fsu.edu/~jburkardt/data/stlb/stlb.html

[...]

a workaround solution could be to look for the keyword "facet" in place of the keyword "solid" [...]

by Alberto Pretto

Related to: !83 (merged)

example file to trigger this issue: sportellino.stl