Here's what you didn't know but now you can expose them.
YouTube decided which they would not like to depreciate the effectiveness of tags as a ranking factor.
So that they started hiding the actual tags on most videos.
If you're looking on your video page source and find out the tags about the "keyword" area of the source.
Then I assure you that most of the time you are not getting the actual tags found in that video.
I can also assure you that more or less all the software you have that pulls video tags for you is doing nothing more than that which you were doing.
Checking in the keyword section for the tags that YouTube says this can be using.