In summary I think it was intimated that the issue might be caused by how XCOM
deals with indices.

===
The game is passing indices outside start..end range, which is illegal per
https://www.opengl.org/sdk/docs/man/html/glDrawRangeElementsBaseVertex.xhtml
"all values in the array indices must lie between start and end, inclusive,
prior to adding base vertex"
===

Mesa Intel and AMD/Nvidia closed source deal with this gracefully by ignoring
the range hint if they are invalid however RadeonSi does not and can in some
cases crash.

Due to XCOM originally being designed for DirectX on Windows where this
behaviour is not a fatal error combined with other OpenGL drivers on Linux &
Mac also not throwing an error/warning this issue was overlooked/missed on the
original port as Mesa RadeonSi was not a supported driver at the time so no-one
saw the issue.

This has already been fixed for our more recent games as the Mesa AMD drivers
now support most of the features needed for many games so they are actively
used/tested/bugs logged at Feral. 

We don't have any plans for a patch in the short term but we'll definitely back
port this fix so we match the spec correctly into XCOM when we next patch it.