It is strange problem. One of the possible reason is something wrong with build path.

New version of Qt creator create a build directory to hold generated source code and object files. (e.g yourprogram-build-desktop) , but old version of Qt creator build on (yourprogram/ or yourprogram/release depend on platform) . If you have tried to build using command line , it also use yourprogram/ .

If you have used command line or old version of Qt creator , it will generate ui_xxx.h in yourprogram/ , and it is always included first. But new version of Qt creator generate ui_xxx.h in yourporgram-build-desktop , but it will use the ui_xxx.h in yourprogram/ in linking. Then the changes of your UI file will not be appear in output program.