BOINC client supports a 1000 WU maximum at which point it receives a message indicating too many runnable tasks to any scheduler request. The 1000 limit is a fuzzy limit. If a client has 999 tasks the scheduler will send enough work to satisfy the request which means the client might have more than 1000 WUs but as long as the number is above 1000, you get the too many runnable tasks message
The limit must be higher now. I've been able to grab over 1200 WCG tasks on 32t machine before.
It's a fuzzy limit... If you have 998 WUs and you increase your buffer by a day or more, you could conceivably get 200 to 300 over the 1000. But it won't get anymore until it drops below a 1000.