Dropping out of model space

I use the layout tab to setup working spaces where layers are controlled
more easily. I do a lot of calculations whilst siting in model space within
a layout tab. In a variety of situations I might do an operation such as
extend a line and the cursor will jump out into paper space. Part of the
linework I have been working on will appear at a point remote from the
drawing area. I simply perform a few undoes to rectify the problem. I am
wondering if anyone else has this problem or is it unique to way I have my
settings
more easily. I do a lot of calculations whilst siting in model space within
a layout tab. In a variety of situations I might do an operation such as
extend a line and the cursor will jump out into paper space. Part of the
linework I have been working on will appear at a point remote from the
drawing area. I simply perform a few undoes to rectify the problem. I am
wondering if anyone else has this problem or is it unique to way I have my
settings