Perforce - build.vcs.number

Hi
My perforce have 4 main branches

proj1 revision@500
proj2 revision@400
proj3 revision@390
proj4 revision@450

my VCS config is set as
//proj2/branches/myproject/ ... //team-city-agent/...

I thought build.vcs.number should return 400, but it is returning 500 instead, and getting incremented when others are checking in to proj1.

There is only 1 VCS root (named DevOps) configured in the teamcity project.

am I missing some configurations ?

I have tried checkout Options like +://prog2/branches/myproject
but it error out like
======
Error while applying patch: Failed to perform checkout on agent: ...@500 - no such file(s).
======

[Updating sources] VCS Root: DevOps (1s)
[19:09:41][VCS Root: DevOps] checkout rules: proj2/branches/myproject=>proj2/branches/myproject; revision: 500
[19:09:41][VCS Root: DevOps] Updating sources for root 'DevOps', revision/label: @500 (1s)
[19:09:41][Updating sources for root 'DevOps', revision/label: @500] Will use p4 executable from 'C:\Program Files\Perforce\p4.exe'
[19:09:41][Updating sources for root 'DevOps', revision/label: @500] Running cleanup of stale Perforce workspaces
[19:09:43][Updating sources for root 'DevOps', revision/label: @500] Running 'p4 sync -f'
[19:09:43]
[Updating sources] Failed to perform checkout on agent: ...@500 - no such file(s).




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EDIT:
Well proj2 in above example is a proj3's new branch and has no change history, once I've merged further change (proj2 has become rev@401) and teamcity started to track correctly.
looks like some "comparison" or "change tracking" bug.