Wicket development mode prevents opening documents

Create a 12.0.0 archetype project.
Add simple content via essentials.
Go to cms
Open a document.
A popup message in red "WICKET AJAX DEBUG" appears.
Document tab is created but no document is displayed

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Edit: issue was caused by a javascript resource cached in the browser (DEVELOPMENT mode only). To prevent these kinds of hard-to-trace bug reports in the future, we decided to add query-string parameters containing the last-modified timestamp to Wicket resources. While query strings are a bad idea in production (they tend to be stripped off) it's fine for local development. Using this strategy has the advantage that the original file names are still recognizable, so it's easy to correlate requests with files in the code base.