If I add a Grid inside pane 1, pane 2 doesn't expand when clicked.

Reproduction: https://blazorrepl.telerik.com/cxkqwAFj38FBkmbP09.

For reference, collapsing and expanding panes works well when adding another component or HTML content: https://blazorrepl.telerik.com/cHEqmAlN35ZSfRKi13.

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ADMIN EDIT

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For the time being, a possible workaround is to alter the configuration to allow the user to resize and expand the pane. Here is an example: https://blazorrepl.telerik.com/mdEKcgFZ45D7rJU013.