When you create a Sideslope, it uses the reference line that you select as its source line and then creates the chorded lines for the sideslope elements based on your interval setting e.g. 2' - there will be two lines at the reference line location - the Reference Line and the chorded line incorporated in the sideslope object. at the offset locations there will only be chorded lines that make up the sideslope object. Any Edits that you make to the Reference Line will instantly be reflected in the sideslope object,
If you make edits to the Reference Line as follows - then you will see these changes to the sideslope object
1) Move the Reference Line using Move command or moving elements of the line using grips - The Sideslope moves with it
2) Add a segment at the start of the Reference Line - the Station 0 moves and so does the sideslope - for simple sideslopes with no tables using stations this will work fine, however where tables are being used, the stations of the reference line changed and the tables remain the same - so the sideslope changes.
3) Add segments to the middle of the baseline - the stationing all changes and the sideslope changes to reflect those changes
4) Break the Baseline - this will truncate the Sideslope object
However ....
If you are applying e.g. a simple Template that has point 1 as a .5,.5 Offset Elevation (TBC) and point 2 that has a 6' 2% Offset Slope (Sidewalk) starting at the end of the line and running the full length of the line - and you join the Sidelsope reference line to the extended line element and you want that same template to apply all the way along the new line then you will get what you want - However as soon as you have table related data where you are varying things by station then you would have to edit all the tables manually because we don't update the values of tables at all because you edited the reference line. Note, you should join the reference line to the line extension and not the other way around - because the Join Process merges the second object into the first and so if the Sideslope references the second line it will disappear after the join because the second line no longer exists.
Note a linestring does not have real stationing - the start of the line is Station 0 always - so if you append a line at the start of a line then Station 0 moves further back, if you add a segment to the end of a line then the end station increases, if you add or remove segments mid line then stationing will overall increase / decrease based on the changes you make - so because of that Tables for Sideslope will get screwed up totally if you make edits to the Baseline - if you are doing complex sideslopes with Tables - get your linework right at the outset - simple sideslopes that apply full length of the line will work well with edits
I think this about covers it - so you can change the source lines as much as you want with zero impact on the sideslope but if you edit the sideslope baseline (copy of source line) then all bets are off - we assume you are doing that deliberately and for good reason
The truncated corner I am sure is caused by a "Computation Interval" getting closer to the corner than the tolerance so we threw out a point and that causes the issue - if you change your computation Interval to a random number say from 2' to 2.15' you will likely see that get fixed - we have that 0.02 tolerance (in next release), and if the corner is at Station 34 and we are computing Intervals at 2' then they match and no issue - if the corner is at 34.01 and we compute 34 by Interval -34 and 34.01 are too close and we ignore one of the points - it
Alan