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I did some research and it appears these differences are by design.
That said, and speaking more generally:
Bug reports and support tickets serve two very different purposes. Support tickets are intended to be a way for you to get help with your account or your character. Bug reports are to let the developers know that there are general problems to fix.
Support tickets and bug reports ask different questions to serve these different purposes. For example, support tickets do not ask for the steps to reproduce the problem you’re describing, but we need those in an actionable bug report. Also, in-game bug reports submit a package of information including game logs, settings, and the state of your game session. So, if there’s an error logged that has to do with the problem you’re seeing (and there often is!) then we’ll see it with a bug report.
The support department can and does pass along bugs that they hear about from support tickets, but because these reports are often missing a lot of this critical information, it varies how much value such reports have.
So please, if you want to report a bug, fill out a bug report. It’s very likely that the relevant team will see your bug report the same day, try to reproduce it if possible, and get it scheduled for a fix.