Qt Creator fails to work with non C++ project files

When I add a non-C++ source files to the project ( lex and bison, .l and .y in this case) files to the project (file are listed in target_sources()), QtC opens them and edits as plain files and even applies some color scheme. Now, after I close and reopen the project, QtC says that those files are not part of any project, and applies clangd diagnostics to them, applies clang-format formatting to them (which, of course, ruins the file structure), and makes it impossible to remove breakpoints in them (it toggles another breakpoint at the same line instead).