Git 'pending changes' + VCS-trigger on change, not running build

I have configured two different projects on two different installations of teamcity on two different servers.

Both are using the rake buildstep and have specified under VCS-triggers, build on change.

For one of them the build is not triggered even though the GUI states that there are pending changes. A manual press of the 'run' button works, however.0

Neither Google nor stack overflow finds answers, nor have I found anything searching this forum...

What should I try?