Select popover interface is not positioning properly

[brandyscarney]

Bug Report

Ionic version:

[x] 4.x

Current behavior:
When the popover is opened on a page that scrolls, the backdrop is not taking up the window height and thus positioning it in the wrong place. This does not happen with the alert interface. See the below images.

popover	alert

This was originally found on our docs site.

[ionitron-bot]

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