Creator becomes sluggish while a qbs build is going on

While building a qbs-based project, Creator becomes noticeably slower to react to user input (scrolling, switching modes etc). This is not due to high system load - other applications on the same machine continue to work just fine. We need to investigate why that happens (according to Tobias, similar behavior has in the past been found to be related to cross-thread signal/slot connections). Once we have verified the cause, we can think about possible solutions.