Had the same issue: removed elements in mainform.ui, recompiled and ran the app. The changes didn't show up. I noticed that ui_mainwindow.h appeared in the project list under "headers". Removed this (with "delete from disk") and everything worked just fine. ui_mainwindow.h showed up newly built in the build directory, where it belongs. So I had two versions of this file, one still defining the form before editing.