If a buffer is at its maximum lines and new text comes in, adding a line or lines to the bottom, *and* if the text buffer is currently shown and user has scrolled it to the top, strange and unpredictable things may happen on mouseovers and while in the midst of selection.
1. /join a channel whose log size is greater than text_max_lines and which has current activity, such as efnet:#philosophy, (or on another box join the same channel, to monitor it and add lines)
2.Scroll to the top of the channel and (on the other box) monitor it (at the scroll bottom) and/or add lines.
3.Mouse over the top few displayed lines at your window scrolled to the top; observe that nicknames, URLs, and such are gratuitously changed
4.Try to select a chunk of lines including the top line; while holding down the left mouse button add lines on your monitoring PC's window; release the button and paste the selected lines somewhere. Note that they don't show the top line(s) selected.
Lines should scroll off the top of a maxxed-out window as they are added at the bottom of the buffer.
The patch fixes the problem. This occurs on svn version 1472.