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When compiling with gcc 4.4.1 on Ubuntu 9.10, I encountered strange display bugs. Apparently, new odd edges appear and strange filling is applied.
The root cause seems to be a gcc bug related to in-place construction of objects. It is pretty hard to pinpoint but so far I would not recommend gcc 4.4.1 for building KLayout.
I have been using gcc 4.3.2 in the past and did not encounter these problems.