In UBB.threads 7.5.x series, the CSS white-space value for "pre" is undeclared. And thus, it was treated as "pre{white-space:normal;}". Its default value.
Here on UBBCentral while running the current UBB.threads 7.6.0 Preview, the /styles/common.css file had been completely rewritten from the ground up. The "pre" value was updated/changed, though there was nothing wrong with it in the first place.
You've found a bug -- thank you!
The change has been reverted.
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The value that was added to 7.6.0 Preview was:
pre{margin:0;white-space:pre-wrap;}
It has now been reverted back to just:
pre{margin:0;}
Again, thank you catching this and pointing it out.