The JavaFX build.gradle logic is composed of a root gradle project and several subprojects. Each subproject that builds a JavaFX module has a "moduleName" property with the name of the module.
Most places in build.gradle use that property, but there are a few places in build.gradle where the build logic derives the name from the name of the project by prepending "javafx." to the name. This will fail for modules with a prefix other than "javafx.". Further there is one place where the logic replaces dots with dashes in the name, but it does so by prefixing the project name with "javafx-" rather than doing a string replacement. This means that a module with more than one dot will only have the first one replaced.
I discovered this while working on the following two RFEs, both of which hit this bug:
JDK-8309381: Support JavaFX incubator modules
JDK-8337280: Include jdk.jsobject module with JavaFX
Both of them need this bug to be fixed, so I am separating it out into its own issue.