I ran across this problem where the opacity variable was operating strangely when my game was online. Basically, it wasn't cutting the user's line of sight properly. If I tried to troubleshoot it in my own test environment, I didn't get the problem. It only occurred when the game was online.
It had very strange "symptoms" (for lack of a better word), but generally it just straight up wasn't reading the opacity variable correctly. I'll include some screenshots from before I updated my BYOND version.
(http://img194.imageshack.us/img194/5564/exampleaf.png)
-I stood facing an opaque tile, and instead of not being able to see past it, this is what the view "cut off" looked like.
(http://img52.imageshack.us/img52/2426/example2r.png)
-In this one, I put a red box on the opaque tiles that surround the room. You'll notice that you can see part of the building placed next to it on the map, which is not intended.
Numbered Steps to Reproduce Problem:
Downloading a version older than 455.1037 recreated the problem on my game (I'm unsure if it's the same for other games).
Does the problem occur:
Every time? Or how often?
It did occur whenever you played.
In other games?
I didn't have the time to go check.
In other user accounts?
Yes.
On other computers?
Yes.
When does the problem NOT occur?
This problem did not occur once I upgraded my BYOND version.
Did the problem NOT occur in any earlier versions? If so, what was the last version that worked?
Because I couldn't recall whether or not I had updated recently, I got a handful of subjects (players from my game) and conducted a test around it. What I deducted, is that anything before version 455.### was not reading the opacity in my game correctly. Anything newer than that (up to 456.1048) functioned perfectly fine.
Here are my results:
Subject 1-
Version #455.1047: Opacity reads fine
Subject 2-
Version #454.1036: Opacity does not read fine
Subject 3-
Version #436.1012: Opacity does not read fine
Subject 4-
Version #455.1047: Opacity reads fine
(Test/Asked to upgrade/downgrade to different version numbers)
Subject 5/Test 1-
Version #447.1028: Opacity does not read fine
Version #454.1035: Opacity does not read fine
Version #454.1036: Opacity does not read fine
Version #455.1037: Opacity reads fine
Version #455.1047: Opacity reads fine
Version #456.1048: Opacity reads fine
My personal conclusion:
I found that this bug was specific to version numbers. Any version before 455.1037 did not display/read the opacity variable correctly. It caused awkward sight variations, and didn't cut off a person's line of sight at the tile like it should have.
In a case like this, if the old versions are at fault, they do not fix the old version, however, if they can add something to a newer client to fix the old ones, they can do that, but they won't go back and fix the old clients if they are broken.