When you start a new drawing and this happens, is that drawing coming from a template? If so, it could be the block definition. That's what Brad is thinking about here, I believe.
The PURGE command is a Vanilla command that you shouldn't really use in ACADE unless you know what harm it could do. We'll help you along with that if it comes to that. At the end of this post, though, I'll give you the basics so you at least know what's up.
That said, here's what I think you should try: Start a drawing and insert the wrong-sized signal arrow. Then, using the command AESWAPBLOCK, update the block. In the dialog for that command, look in the middle area for 'Option B - Update A Block' and select 'Update a block'. Then, click on the signal arrow and hit enter. Does the arrow change size? It should, because you said that your NFPA symbol is OK. If not, post back with the results. Post the template file too, if you're using one.
If that doesn't seem to be the problem, we'll show you how to see which icon menu your ACADE is currently using, and its location, because I feel like that's the next thing in trying to figure this out.
time for school....
BLOCK BASICS & PURGE: When you insert a block in this software, it works just like it does in Vanilla ACAD. It first reads the source file, then copies that information into your drawing, and finally inserts it. When the file gets copied into your drawing, it becomes something known as a 'block definition'. From that point forward, if you want to insert that same block or symbol again, ACADE won't return to the source file, it will refer to the block definition to get the information it needs.
If you make edits to the source file of a block, they don't just show up in the drawings where that block resides. If you want that to happen, you have to first delete all instances of that block from your drawing, and then use PURGE to remove the block definition. Finally, at that point, if you try to insert that block again, ACADE is forced to go to the source file for the information and it will now reflect those edits you made.
Brad mentioned PURGE because it seems likely that your 'new' drawings are coming in with some block definitions that are wrong.
But ACADE has this great tool that sort of does that whole workflow in the background - the Swap/Update Block command. That's the AESWAPBLOCK command I wrote about above. Try that because it's easier.

Jim Seefeldt
Electrical Engineering Technician