CompletableFuture.thenAccept can indeed block

Unlike stated in some blogs(e.g. I can't emphasize this enough: thenAccept()/thenRun() methods do not block) CompletableFuture.thenAccept can indeed block. Consider the following code, uncommenting the pause method call will cause thenAccept to block:

CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
    log.trace("return 42");
    return "42";
});

//pause(1000); //uncommenting this will cause blocking of thenAccept

future.thenAccept((dbl -> {
    log.trace("blocking");
    pause(500);
    log.debug("Result: " + dbl);
}));

log.trace("end");
pause(1000);

Can we be sure that the following will not block? It's my understanding that if the supplyAsync runs immediately then the thenAccept could block, no?

CompletableFuture<Void> future = CompletableFuture.supplyAsync(() -> {
    return "42";
}).thenAccept((dbl -> {
    pause(500);
    log.debug("Result: " + dbl);
}));