Safari Technology Preview (Release 65) and Safari (Version 12.0 14606.1.36.1.9) are installed in parallel on my iMac. I noticed this behavior which happens every time I try this:
1. I start Safari Technology Preview
2. I click on the 1Password Plugin Icon in Safari Technology Preview
3. not only the 1Password plugin gets displayed, the released version of Safari is launched and appears on screen
4. When I type something into the search field of the 1Password plugin and hit return, the resulting web site is opened in both versions of Safari and 1Password fills in the login information in both Safari versions.
When I start the released version of Safari and use the 1Password plugin, the Safari Technology Preview is not started. Both Safari and Safari Technology Preview have the same version of the 1Password plugin installed.
I am using Safari and Safari Technology Preview for quite some time and have also used 1Password beta versions a lot. I have seen this behavior only in the 7.2 Beta.
iMac Retina 5K, 27-inch, 2017, 4,2 GHz Intel Core i7, 64GB 2400 MHz DDR4, Radeon Pro 580 8192 MB
macOS 10.14 (18A389)
Safari 12.0 (14606.1.36.1.9)
Safari Technology Preview Release 65 (Safari 12.1, WebKit 14607.1.5.2)
1Password 7 Version 7.2.BETA-2 (70200002)
1Password Plugin 7.2.BETA-2 from Password 7
1Password Version: 7.2.BETA-2 (70200002)
Extension Version: 7.2.Beta-2 from 1Passoword 7
OS Version: 10.14 (18A389)
Sync Type: iCloud