WebUI hangs completely and becomes unresponsive with this prompt [reproducible bug]

[arsaboo]

Bug Report

WebUI becomes unresponsive

Description

Bug Summary:
The following prompt leads to all sorts of issues in WebUI

What is the difference between using 

Here is the first 4096 characters of the query:
{{prompt:start:4096}}

Here is the last 4096 characters of the query:
{{prompt:end:4096}}

vs using 

Here is the query:
{{prompt:start:4096}} {{prompt:end:4096}}

for prompt generation?

The CPU usage shoots up

and then the page becomes unresponsive:

This is entirely reproducible - just try the prompt.