Hadn't opened jEdit on Mac in years, updated to the latest version today and tried to reproduce the error. Most of the time it works as expexcted, but just now I switched back to it and got the opposite problem: the arrows worked, but letters didn't, until after I clicked. "jEdit 5.5.0 server-background mode, using Oracle Corporation Java 1.8.0_172" on macOS 10.13.6 (17G2112)
Still occurs in jEdit 5.1.0 server-background mode, using Apple Inc. Java 1.6.0_65...