Note the error here is an _assertion_ in libxcb rather than a segfault. That implies that it's not a bug in the library itself, but rather that the library is catching a fault that probably originated elsewhere in the stack.
Possibly this is similar to or even the same as bug #833694, which appears to be fixed upstream but not in ubuntu. In particular see this comment on the upstream bug, which explains what happened in the client code that cause this assertion to get tripped: https://bugzilla.gnome.org/show_bug.cgi?id=657255#c8
Note the error here is an _assertion_ in libxcb rather than a segfault. That implies that it's not a bug in the library itself, but rather that the library is catching a fault that probably originated elsewhere in the stack.
Possibly this is similar to or even the same as bug #833694, which appears to be fixed upstream but not in ubuntu. In particular see this comment on the upstream bug, which explains what happened in the client code that cause this assertion to get tripped: https:/ /bugzilla. gnome.org/ show_bug. cgi?id= 657255# c8