Strange behavior with USPS website

Brave 0.22.669
V8 6.6.346.24
rev 6cda2e8
Muon 5.2.7
OS Release 16.7.0
Update Channel Release
OS Architecture x64
OS Platform macOS
Node.js 7.9.0
Brave Sync v1.4.2
libchromiumcontent 66.0.3359.117

macOS Sierra

I’m not actually sure what’s happening here but I just had reason to submit a complaint about a postal carrier via the USPS website:

With shields turned completely off, after filling out all the form options I hit submit and a blank Brave window pops up. But nothing further happens. I have no idea if anything was actually submitted or not, as there is no way to tell. The underlying form page remains and does not change.