Hi,
I detected a bug in the Perform dialog. And I will explain how to reproduce the problem:

1: Open mIRC options
2: Select Connect / Options
3: Click on the Perform... button
4: Click on the Add button
5: Select the network and click OK
6: With the network selected, type something into the edit box
7: Click the Add button again
8: Select a new network and click OK
9: With the network selected, type something in the edit box
10: Without closing the dialog, click on the combo and select the first chosen network

After selecting the first network, we see that the edit box is empty and what we had previously typed has disappeared.

This has been tested on mIRC version 7.75
Windows 11 Pro 22H2 (OS Build 22621.2215)

Thanks this issue has been fixed for the next version.