It was ultimately determined that labels which were taller than they were wide (e.g. short multi-line labels) caused the alignment to shift to the left beyond the insertion point.
This was due to code that was attempting to account for tall-narrow labels fitting inside of rounded frames, but was executed even if the label was not framed, or did not even have rounded ends.
In addition to correcting (removing) the erroneous code, changes were required to properly draw rounded and pointed rectangles so as to fully contain the specified text.
Note that there are still some issues with the drawing if Frame Transparency is enabled, but these could not be resolved in this iteration.