Make sure that the package's "Execute before" entry is blank.
@Pascal, please remove the "Execute before" or change it so it compiles on Linux and other platforms.
This revealed also a usability problem with OpkMan. It does not allow opening the downloaded (broken) package in the IDE. Some of the toolbar buttons operate on selected packages but some don't. For example you would expect the "Open" button to open a selected package but it does not! Clearly there should be 2 visually separated toolbars.
@Pascal, you could also add "$(IDEBuildOptions)" to the compiler "Custom Options" of your package. Then it is built with the same debug flags as the IDE itself. It would allow people to send you backtraces of errors better. A backtrace may be enough to find a bug.
Actually Bram71 already has range check enabled as he got an "index out of bounds" error.
Anybody testing beta or development versions should enable all debug flags and checks.