Eclipse Plugin does not show @ in sidebar for annotations that have not been compiled this session

When opening a workspace that that contains java sources that have previously been compiled with the Backport175 Plugin enabled the Annotations don't show the @ in the sidebar when the source file is opened, even 'though the corresponding class file still contains the Annotations. When the file is recompiled the @ re-appears.

This problem is especially troublesome as sometimes the plugin seem to get confused during full compiles (or partial ones, I can't yet reproduce it reliably) and with this bug it's getting very hard to diagnose this kind of problem.

I will try to find the cause of this problem, but I can't promise anything as I've never built a Builder Plugin in Eclipse (only simple GUI/text manipulation plugins).