Build blocker does not support jobs in relative folders when job description is set. For example:

RootFolder
– SubFolder1
-> Job1 (description "Job Description")
– SubFolder2
-> Job2

I cannot use followin expression in Job2:
../SubFolder1/Job1

Only this works:
.Job Description.
but this is not solution.

Expected result:
This works:
../SubFolder1/Job1

When Job1 is building then block Job2