Yes, I suppose we should not fall back to the TCCL when detecting whether JavaFX is available or not, it's really the classloader of HV's classes which must be able to access the JavaFX types.

I am surprised though that your TCCL can "see" the JavaFX types, whereas the HV classloader cannot. This post may be helpful, it may be that the JavaFX packages are not properly exported by the system bundle (see section "Importing JavaFX packages"). So another workaround would be to make sure that these packages are exported.