Lightroom 7.x broke the ability to show placeholder_string in text input fields created by LrView.osFactory():edit_field and password_field.
This is visible e.g. in Hard drive publish service description fields, first Lightroom Classic CC 7.3.1 and then Lightroom 5.7.1 (sadly I couldnt run 6.14 concurrently with latest release, all I got was error 1 on startup)
LR 7.3.1: RackMultipart20180511928191c5a-b7b86908-0c29-4a68-9093-bbcd3d2539e2-807507256.png LR 5.7.1 RackMultipart20180511106236hw6-6e17e0bd-0a2f-4a2f-9293-e66bc4d294f8-709743792.png
As you can see, the placeholder string "Untitled export" is not visible in Classic CC, and so are not any other placeholder_strings. I think this used to work fine in 6.x, and I've used for example login/password fields in my plugins. Now the users are pretty confused because all they see is empty text field.
Tested on Lightroom 7.3.1, macOS 10.13.4. Sorry, didn't try it on Windows.