Created attachment 104928 [details]
It shows the cursor one line down from the top.

I am on kubuntu, so I get the kate (and kwrite) version the ubuntu people give me.

I have been using kwrite to maintain a big file (25 mb). (Note that kwrite uses the kate editor.)

On kubuntu 14.04 (kate version 3), kwrite worked great.

When I first tried kubuntu 16.04 (kate version 5/15) in early 2016, kwrite was clearly not the same:

1. For the arrow keys, keyboard repeat works at the top of the file, but not further down. In kate version 5/15, the display does not update -- you cannot see where the cursor is. If you hold an arrow key down for a while and release, after some seconds, the cursor freezes then reappears somewhere. In kate version 3, anywhere in the file, you see exactly where the cursor is at every instant, you can release the arrow key when you want, and the cursor is where you expect it to be.

2. Pasting text into the file (anywhere except the top), kate version 5/15 takes several seconds for the text to appear. Using kate version 3, the text appeared instantly.

After evaluating kubuntu 16.04 in early 2016, the kwrite problem was a show stopper -- I declined to upgrade kubuntu, and I have been on 14.04 until recently. But then in March, a more pressing consideration made me upgrade to 16.04, and kwrite is still a problem on my big file.

In 2016, I tried tweaking settings in hope of fixing the problem, but I did not find a solution.

Note that I encountered this problem using the same hardware.  Right now, I have two hard drives for my Lenovo Thinkpad T500 laptop with 8 GB memory, one hard drive with kubuntu 14.04 (kate version 3), and another hard drive with kubuntu 16.04 (kate version 5/15).  I can shut the laptop down and swap hard drives. You can say my laptop is too slow, but kate version 3 works perfectly OK on my laptop -- no complaints.  But on the same laptop, kate version 5/15 sucks.

I have encountered deniers, so I assembled a big file -- anyone can try it themselves.  I googled "Richard Stallman", went to some hit pages, and copied some text by or about him. I pasted into a file and duplicated. I used the fmt utility to break the long lines into shorter lines (the file I edit in real life has mostly short lines). The file is almost 27 mb (too big to attach). I gzipped it, and uploaded it here:

http://www.advanced-app.com.hk/MiscJunk/Stallman_Richard_short.txt.gz

For both the following tests, I used wget to download the file and gzip -d to extract it.

For the latter of the two tests below, see the attached picture. It shows the cursor one line down from the top.  The test, conducted near the bottom of the file, is to determine, after pressing down arrow once, how long it takes for the cursor to appear one line down from the top (as explained in detail below).

On the Lenovo Thinkpad T500 laptop with 8 GB memory running kubuntu 16.04 (kate version 5/15):
I went to the bottom of the file, and from the bottom I selected up to and including the line "The consequences:". I copied the selected text. I used PgUp several times until I came to the heading "The GNU Manifesto". Above that heading, I hit Paste (Ctrl-V), and counted "one thousand one, one thousand two, one thousand three, ..." The inserted text appeared between one thousand five and one thousand six. I hit Ctrl-Z. I pressed the up arrow key, and kept pressing it while I counted ""one thousand one, one thousand two, one thousand three, one thousand four, one thousand five" then I released the up arrow key, immediately pressed down arrow once (quickly) and started counting again. The cursor did not appear one line down from the top until AFTER I counted up to one thousand eight.

On the SAME Lenovo Thinkpad T500 laptop with 8 GB memory, running kubuntu 14.04 (kate version 3):
I went to the bottom of the file, and from the bottom I selected up to and including the line "The consequences:". I copied the selected text. I used PgUp several times until I came to the heading "The GNU Manifesto". Above that heading, I hit Paste (Ctrl-V). There was no need to count, as the inserted text appeared instantaneously (to my human perception). I hit Ctrl-Z. I pressed the up arrow key, and kept pressing it while I counted ""one thousand one, one thousand two, one thousand three, one thousand four, one thousand five" then I released the up arrow key, immediately pressed down arrow once (quickly). There was no need to count again, as cursor had come to a stop instantaneously after releasing the Up arrow, so the cursor moved down to the second line immediately after pressing the Dn arrow. While I was pressing the up arrow key, the cursor never disappeared, but moved up smoothly and continuously.

Same results using kate and kwrite.  Exactly the same resuls on different computers -- on big files, kate version 3 is fine, kate version 5/15 sucks.

My hope is the problem can be fixed, that kate version 5/15 can be a good on big files as kate version 3.