I was debugging something which flood-echo debug line in status window, this is from a very fast timer.

In previous version of mIRC, I could easily go to the status window, give it a small scroll up, and the scroll would go up as expected and stay there meanwhile the window is still receiving massive amount of lines, aka it would not scroll down automatically.

This is no longer the case on 7.66.

Now I can barely get mIRC to stop scrolling down automatically, depending on the speed/amount of lines getting echoed: it's nearly impossible to manually scroll up to get it to stop scrolling down, in my specific case which made me write this report, even holding the page up key will not work, even holding control + start won't do it unless you held it for a while (same for page up depending on the number of lines).

Here is a script that more or less reproduce my case, you can add more echo to get more lines, this sample is enough to show the problem for me:

Thanks for your bug report. There have been no changes to how timers work or to the way text is displayed in v7.66. If you are using a /timer to display text at a fast speed, it is very likely that the timing of events have created a situation where window messages, timers, key presses, etc. are all being processed in a certain sequence.

I assume no change happened to the ordre of processing Windows messages as well, but once the scrolling message is processed, it should be scrolling up and never go down, if that is the intended behavior, so I feel like something changed somewhere.

Khaled changed the default /fupdate value to 95. This will change the behavior of how mIRC updates the scroll buffer. Instead of going line-by-line, it will now blaze by in pages when it begins to backlog on your slow computer.

Try On *:START: fupdate 0 since you preferred the old sluggish behavior.

I just tested your script and the behaviour is present in all versions of mIRC that support /fupdate, back to v7.52. /fupdate itself uses a timer, so the issue is your timer, the /fupdate timer, and key press messages, arriving at different times. I might be able to find a way around this for the next beta.