Our project is using a variable to specify the local repository directory for Git, such as "${var}". When triggering builds with Git hook, GitSCM.compareRemoteRevisionWithImpl() uses it's plain text value to retrieve the working directory, eg "workspace/${var}" instead of "workspace/dir". As a result, hook always think new change is found and trigger new builds even there is no new change at all.

I did some debugging and found that the environment variables retrieved when triggered by hooks are less than those when triggered by "Build Now". But I could come up with a quick fix.