Ok, turns out that editing works. It's just that you can't tell where the underscore is at (since it's always displayed under the cell's ID).

Here's an image (including a zoom) to demonstrate the problem.

uhm well it seems a nice error. but i don't have lotus.

you could try the debug version of dosbox.

start the application.
when it's running press pause
go to the other window.
enter this:
<return>bpint 10 *<return>f5
edit a cell.
dosbox should halt.
note the number in ax (at the top)
press f5
repeat. till it runs again.
tell us the numbers you noted down.

First of all, I use the standard "binary" DOSBox version - does it have debug options?

I've tried pausing, pressing alt+tab for the DOS window and entering what you said. Is there supposed to be a space there between "bpint", "10" & "*"?
Anyway, nothing special happened when I unpaused.

Is there any chance I can give you the app?

DOSBox debugger

yes there are spaces between the bpint 10 *

Alright, I've downloaded the debug version and got to the part of "dosbox should halt".

...except it doesn't halt! As soon as I type your command, it's as if I just pressed "pause" again and so the app is just unpaused.

Also, when you said AX, did you mean EAX (on the top left corner)?

the game doesn't use int10 while running.
it programs the vga registers directly and doesn't update the int10 bios part.

This causes the problems. (as the mouse cursor uses the int10 bios data to)

I fixed the mouse so that it doesn't use those data anymore.
Now it works allright.

Wow, Qbix has already fixed it in the CVS!
Thanks, Qbix! 😀

I'll report back once it makes it in the official DOSBox.

Just wanted to confirm that the problem is indeed fixed in DOSBox v0.65.