I am using PSD v15.0.0.2050, 64-bit. When I try to view package body I'm getting /* Source of PACKAGE BODY MILK.GM_EXT is not available */, but when logged into the same database as the same user using SQL Developer I can access the package body. See both screen shots attached.

Just one point of clarification - the issue arises when I am logged in as a user other than the package owner. If I log in as the package owner, the package body is visible. Is there a security setting that PL/SQL Developer is obeying that SQL Developer is not?

Perhaps you need to enable the "Use DBA views if available" option from the Oracle > Options preference page? Now PL/SQL Developer will use the sys.dba_objects, sys.dba_source, etc views instead of the "sys.all_xxxx" versions.

You will need to restart PL/SQL Developer before this preference change takes effect.

Thanks Marco, that option was already ticked, but I played around with a few other settings, shut down PSD and started it up again, and now it's working fine - I cannot recreate the issue no matter what settings I apply. So you can ignore this issue, unless it recurs.