When i run this code in a Mac with Lazarus 1.8.2 i get the old value of the combobox when i change it.In 1.8.0 i get the chosen value.That is the problem i have. I posted this so anyone else can try and get the same result as i have. Then we know that it is a bug
On June 28, 2017, Apple announced that 32-bit software for macOS, such as all Carbon applications, would no longer be supported “without compromise” on versions of macOS after macOS 10.13 High Sierra and only 64-bit software (which excludes Carbon) would run natively on versions of macOS that come after High Sierra.