I do not really have an answer for you - sorry. I am posting only because yesterday for the first time ever, I was dimensioning a part and noticed the value was really wonky. So I learned that the dim was "true" - I had never before heard of that. I finally was able to set it to "projected" and everything was fine.
Two thoughts for you:
1 - I noticed also the the arrow head font was slightly different with a "true" dimension - it was shorter or more squat than the normal arrow head. So, I think you CAN tell if the dim is true or projected - maybe that is your warning...
2 - SWX help says that this is set based on the type of view (aux, projected, orthogonal, etc...) and can be changed in the dim's property manager. I saw no mention of a setting to control it globally.
I never noticed it before! I will use it for sure when I can notice it!
It probably happens when there is a big depth difference between the two snapping points. The dimension arrows are point in depth instead of linearly. The deaper the snapping is, the shortest the arrow will look.
In most of my cases, there is slightly a plate's height difference, and the arrow looks exacly the same. See example:
"Thanks for any help end suggestion!"
"Thanks for any help and suggestions!"
I probably made others but that one annoyed me...sorry