This weird add node behavior is similar on all types of TC elements. Interestingly, the next morning after starting this post, the edit mode functions now work differently again. Without changing any settings, opening the exact same file as I was working the other day, selecting, modifying and add/delete node functions all work as they originally did. A behavior I have not seen in over a month.
Being a programmer for 30 years, I have never seen an application, even in development that changes it's operating characteristics as randomly at this one. I really would like to figure out the cause of these weirdness's, and I'll admit I only I have about 2000 hours of experience with this application, but I struggle with the numerous behavioral oddities just about every day.
I have searched for a technical description of the software data structure, properties and constraints so I can understand some of these problems, but have had no luck.
Anyway thanks for the replies.