https://bugs.gentoo.org/655320
https://patchwork.kernel.org/patch/10382199/

--- dash-0.5.10/src/jobs.c
+++ dash-0.5.10/src/jobs.c
@@ -975,8 +975,8 @@
 	int st;
 
 	TRACE(("waitforjob(%%%d) called\n", jp ? jobno(jp) : 0));
-	while ((jp && jp->state == JOBRUNNING) || gotsigchld)
-		dowait(DOWAIT_BLOCK, jp);
+	while (jp ? jp->state == JOBRUNNING : gotsigchld)
+		dowait(jp ? DOWAIT_BLOCK : DOWAIT_NORMAL, jp);
 	if (!jp)
 		return exitstatus;
 	st = getstatus(jp);