Bridges changing position after saving?

Bridges have been giving me trouble lately, which sucks because they play a major part in my map design.

I had my first problem while trying to place a bridge parallel with the top of a double box to make a sort of balcony along the box's longest edge. At first I did this by putting two bridges perpendicularly across the top of the double box, with their ends sticking out. Using their undersides as a brace, I took a third bridge and raised it up from underneath. If everything went well, then the bridge would be aligned evenly with the box in all three dimensions.

Once the bridge was in this perfect position, I'd save as a new map, quit, then load it up again to delete the braces. But upon loading, I found that the bridge had shifted slightly, and was at a noticeable angle relative to the edge of the box, leaving a significant triangular gap in what was supposed to be a seamless floor.

I thought this was some odd problem with the "save and quit" technique, that if an object was under tension when saved it would shift slightly upon loading again. I didn't think much about it, though, since I soon discovered an easier method of making the balconies*.

But the shifting problem returned in a much more noticeable way just now. I'm trying to make a street-like divider for my map, and I'm using a line of upside-down bridges to do that (their black undersides look a lot like asphalt). Since the "street" would be very long, almost reaching across the map, I used interlocking to make the bridges as parallel as possible. Once satisfied with their alignment, I saved the map. I then made an experimental change to an object that I wasn't happy with, so I quit and reloaded.

I was shocked to find that all my bridges were out of alignment. I thought that maybe I'd saved improperly, or just forgotten, so I realigned the bridges and then saved again. On reloading, they were all out of line. Again. Each one had rotated slightly, turning this:

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into this:

//
//
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Anybody else have trouble making interlocked bridges stay in place after a save? Is there something odd about the floor that I'm not compensating for? What's the deal?

* (Take a second double box and turn it on its side, pressing the flat bottom of the box against the side of the first one. Because boxes are slightly taller than they are wide, the upper surface of the sideways box will be a little lower than the top of the first one. Luckily, this height difference is equal to the height of a bridge, so placing one on top of the second box will make the top of the bridge even with the top of the first box. Just delete the second box, and you're done!)

 

Alright, this is getting really weird. I took two bridges -- one right-side-up, one upside-down -- and placed them directly on the ground, not touching any other object. I also made sure they were parallel with the markings on the floor so I could tell if they moved.

I saved the game, then started a new round. They were still in place.

I set them to spawn ten seconds after the game started, then started another new round. They both spawned, still in place.

So finally I quit, then immediately started a game on the same map.

Both bridges were out of alignment.

So, WTF basically.

Has anybody seen this problem? Any ideas?

 

One last bizarre turn of events:

I placed a bridge upside-down on the ground as before, aligning it with the floor markings. I then took four fence walls and laid them flat on the ground, with their top edges braced against the sides of the bridge. After saving and then starting a new game, I found that the bridge was once again out of alignment, and had in fact merged partially into the fence walls on either side. So, whatever is causing the movement, not even immobile objects can stop it.

Oh, and I can now confirm that this problem isn't caused by the floor. I just now placed a bridge on top of a double box, aligned with its edge. Save, quit, start again, and presto! The bridge is now rotated out of alignment.

I'm stumped. Do bridges just not stay in place ever, and I just now noticed?

 

Nah, I'm by myself right now.

What's really strange is that it happens when starting a new game, but not when starting a new round. What's the difference? They're both spawning immediately at the start of the game.

Apologies. The last two messages I posted were made one right after the other (I've got my laptop right here by the Xbox). I was so annoyed by what was going on that I didn't think to just edit the new information into my other post instead of making a new one.

(Besides, is it really bumping if you reply to your own thread so quickly that it's still at the top of the forum when you do so? )