We have our C++ code in files named ending in .C and corresponding header files end in .H.
In Qt Creator 9 and earlier, the file would be opened according to its path is on disk. As of Qt Creator 10, the file is opened as if its extension ends in .h (lower-case 'h') even though no such file exists this way on disk. It will display the file's contents fine, but if the file is saved while it displaying the extension with the wrong case, Qt Creator renames the file on disk to the wrong case. This makes F4 completely unusable for us. If the corresponding .H/.C file is already open in Qt Creator then the problem does not occur.

I suspect https://codereview.qt-project.org/c/qt-creator/qt-creator/+/465742