Some troubleshooting thoughts (I can't say that I've observed this and as I am at work, am unable to test):
Try it with ALL mods disabled (if any were enabled)
Completely dump the game from your PC and then reload it from Steam. Note: I'm not talking about file verification from Steam. I mean uninstall/delete all files associated with the game, including everything in the "Documents/My Games" area and any straggler files after uninstall in the "Program Files/Steam/SteamApps" location. Make sure to save copies of any mods/saved games/etc you want, but don't reload them in until after you've had a chance to test if the problem has cleared up.
While I doubt this is the cause, try to update your graphic's drivers anyway. It may (potentially) even be a situation where you need to downgrade the drivers to a much older one (Knights of the Old Republic had this issue with nVidia).
I'm also curious if this problem ever cleared up for you between versions 1.03 and 1.82?
First I want to thank you and Seleuceia for the detailed tips. I haven't actually played the game between versions 1.03 and 1.80 because I was too busy with other stuff. If I play a replay from the "pro" thread (http://forums.sinsofasolarempire.com/454491/page/1/#3469005), I see the Advent corvettes there fire all their guns, sides and rear included. (There is indeed a graphics difference between these two, though not a big one; the side guns seem to shoot more densely spaced blobs.) So it seems the problem is only in my own SP games rather than a general graphics issue with the game. I'll upload a short recording (30s or so) from a SP game of mine and maybe someone will be kind enough to tell me when they play back whether they see the rear & side guns shooting or not...
Alas, if I disable all mods, the vettes spawned with dev exe seem to shoot fine with all their guns. But my SP games use the Artificial Unintelligence mod (http://forums.sinsofasolarempire.com/451274/page/1/) because the SP AI/game is way lame otherwise. It would be strange if that mod causes the graphics to glitch (does no modifications to corvettes that I can find). Alas I cannot load save games that use[d] that mod with the mod disabled; doing that crashes/minidumps the game engine...
Strangely enough, I experience the problem during gameplay in the production exe even with all the mods disabled, but not in the dev exe, unless I'm watching a recording created with the production exe. So, I've uploaded a pair of save/recording to http://www31.zippyshare.com/v/69411389/file.html, which requires no mods to load (both were created with zero mods enabled, albeit the save game was made with the dev exe in order to save time, and the recording was made with the production exe, which is the only one creating issues for me now). In the recording I see the Advent vettes at the Vasari homeworld fire only their main beams (it doesn't matter for me with which exe I watch the recording with). On the other hand, if I load the save game in the dev exe, the vettes start shooting their other guns too. I'd be grateful if someone can test the following (neither should take more than a minute):
- does playing back the recording (doesn't matter in which exe) in your installation show any side/rear guns of the vettes firing?
- does loading the save game in your production exe result in the vettes firing all their guns?
Thank you in advance.