Replace replaces wrong block of text when Word Wrap is on and search term is after 9,250 (approximately).
Reproduced in 6.4.3 and 6.4.5 UNICODE on Win 8 Enterprise x64.
I can reproduce it on 2 Win 8 PCs, but not on Win 7 (I did not try other OS), so I assume this is Win 8 only issue.
Try attached sample text file. Make sure Word Wrap is on. Use Replace to search for 'test' and replace it to 'tt', Search Mode Normal. Click 'Find Next', then 'Replace'. (text in file does not matter, replace term does not matter, Match case does not matter). The problem starts when search term is after 9,250 column. The problem does not occur if Word Wrap is off. The problem does not occur when click 'Replace All'.
Instead of replacing 'test' near the end of file, it replaces previous line (first for this sample file).