I have still not been able to reproduce this issue - I think we will need to go through this step by step, so that we can pinpoint exactly where the issue is occurring. Here are the steps I am following:
1. Copy the mirc.exe from v7.14 into a new, empty folder, with no other files, scripts, or settings.
2. Create an empty mirc.ini file, with no settings, in the same folder as the mirc.exe.
3. Run mirc.exe
4. Enter a random nickname when the options/connect dialog appears.
5. Open the Options/Ports dialog.
6. Enable the "Bind to Adapter or IP Address" checkbox.
7. Enter IP address 111.222.111.222 into the editbox.
8. Click the OK button.
9. Click the OK button in the Options dialog.
10. Type /server irc.efnet.org to connect to a server.
11. Once connected, type //whois $me to whois yourself. The whois reply should show your real IP address as seen by the server.
12. Type /quit to disconnect from the server.
13. Open the mirc.ini file in a text editor and check the [ports] section. The IP address should be saved correctly in both adapter= and address=.
14. Run mirc.exe again.
15. Open the Options/Ports dialog again. The IP address should still be set correctly.
If you follow the above steps, at which point do you see the issue? Please follow the above steps exactly.