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Did Sig change the recoil spring design??

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Hello everyone. I added an M18 to the collection this weekend and disassembled it for the first time today. Upon installing the slide back onto the frame, I ran into a problem in that the slide would not go back far enough to engage the slide lock. Upon searching the web and this forum, I found that the recoil spring should be oriented so that the FLAT sides are oriented VERTICALLY on the barrel lug. Well, I made sure to install it like that and the slide just will not go back all the way. I decided to orient it the other way, with the FLAT sides HORIZONTAL and it went back together just fine and the slide functions perfectly. This contradicts every how to video or forum posting of how to install the recoil spring. Did Sig change the design?

As you can see in the pictures, with the spring oriented with the FLAT sides VERTICLE, the rod is crooked with the slide as far back as it will go (which is just before the slide lock can engage). However, when oriented with the FLAT sides HORIZONTAL, the slide goes all the way back and the rod is straight.

Anyone want to compare theirs (especially if its new)?