Round corner-Filter has problems with first node

On short segments the round corner-filter has problems, if it is used on the first node. the filter can’t move the first node more than the half length of the segment.
In the screenshot the square form is 60×50 units, the round corners are 44×25 units (top) and 30×44 units (middle).
On regular nodes there is no problem (44×44).

I fixed it.