VHOST discovery does not work when using proxy

[tauh33dkhan]

gobuster vhost discovery does not work when using proxy such as burp suite.

• Output without using proxy, here it is working as expected.

$ gobuster vhost -u http://forge.htb -w wordlist.txt                                                                          1 ⨯
===============================================================
Gobuster v3.1.0
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@firefart)
===============================================================
[+] Url:          http://forge.htb
[+] Method:       GET
[+] Threads:      10
[+] Wordlist:     wordlist.txt
[+] User Agent:   gobuster/3.1.0
[+] Timeout:      10s
===============================================================
2021/12/09 13:58:16 Starting gobuster in VHOST enumeration mode
===============================================================
Found: dev.forge.htb (Status: 302) [Size: 279]
Found: support.forge.htb (Status: 302) [Size: 283
Found: test.forge.htb (Status: 302) [Size: 280]   
Found: admin.forge.htb (Status: 200) [Size: 27]   
                                                  
===============================================================
2021/12/09 13:58:18 Finished
==============================================================

• Output when using burpsuite proxy

$ gobuster vhost -u http://forge.htb -w wordlist.txt --proxy http://127.0.0.1:8080
===============================================================
Gobuster v3.1.0
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@firefart)
===============================================================
[+] Url:          http://forge.htb
[+] Method:       GET
[+] Threads:      10
[+] Wordlist:     wordlist.txt
[+] Proxy:        http://127.0.0.1:8080
[+] User Agent:   gobuster/3.1.0
[+] Timeout:      10s
===============================================================
2021/12/09 14:04:43 Starting gobuster in VHOST enumeration mode
===============================================================
Found: admin.forge.htb (Status: 200) [Size: 1352]
Found: dev.forge.htb (Status: 200) [Size: 1350]  
Found: support.forge.htb (Status: 200) [Size: 1354]
Found: qa.forge.htb (Status: 200) [Size: 1349]     
Found: test.forge.htb (Status: 200) [Size: 1351]   
                                                   
===============================================================
2021/12/09 14:04:45 Finished

Now it gives completely different output and if I look at the burpsuite http history the request never went to the server but still gobuster is showing size and `200` status in the output.

Then I used wireshark to monitor packets while using proxy and it shows that only one request to main host `forge.htb` was sent but gobuster is showing `200` response for all the vhosts with diferent size.