i changed the subject because this error has nothing to do with a
"cursor" object.

description: a struct displaying an array (size 1000 x 512)

updating/changing the struct/array goes awry when the changes come to fast.

as prevention a minimal delay time between changes is used.

i've made an (new) automated patch to test the minimal dealy time
needed (in my case). (zip attached)

with Pdext 42.5 it can be as low as 5 msec without getting stuck.

idem with Vanilla 46.4.

with Pdext 43.4 even with 100 msec Tcl errors occur and after 2 errors
or more the patch gets unusable.

to me this looks like a bug.

(i'm on Windows 7)

rolf