Fragments editor dumps stacktrace on syntax error in editor, unhelpful UI error message

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 7.1.10 DXP FP5, 7.2.0 Beta 3
• Fix Version/s: 7.1.X, Master
• Component/s: WCM > Fragments
• Labels: None

Found out during reproduction of Christoph Rabel's forum post:

When editing a fragment HTML with Freemarker elements, any (temporary) error (due to the preview being generated if the typing break exceeds a few milliseconds) will dump a huge amount of stacktrace (60kB in DXP 7.1 SP1, 27kB in 7.2 B3) onto tomcat's console, while the editor is left with a nondescript error message (DXP 7.1 SP1: "Page Fragments is temporarily unavailable."; 7.2 B3: "An unexpected error occurred")

Screenshot made on 7.2b3, apart from the actual error message text it's "the same" as in 7.1. Attaching out71.txt for DXP 7.1 SP1, out72b3.txt for 7.2B3