I reproduce it on forge projects (git://github.com/forge/core.git forge).
EXECUTE 1: Start studio and create test class Test in forge-shell-api project.
EXECUTE 2: add injection field @Inject String a;
ASSERT: Warning appears (No eligible beans).
EXECUTE 3: change field to @Inject Test a;
ASSERT: Warning disappears, open-on to bean Test works.
EXECUTE 4: clean/build the entire workspace
EXECUTE 5: repeat steps 2 and 3 several times and check asserts.
ASSERT: open-on to bean Test works when type Test is assigned to field a.
FAILURE: Warning does not appears when type String is assigned to field a.a
If failure is not reproduced, try and rebuild workspace again (probability of the failure is high).