Query Builder error when using worksheet tabs

Now and then, when I click on a worksheet tab to focus it, I get a pop-up dialoque with a Query Builder error:

Text is not a valid, single SELECT statement.
QB-ERROR: NullPointerException
Query Builder disabled.
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at com.adbs.ast.AstNodeBase.getMyChildren(wc:166)
at com.adbs.ast.SQLSubQueryExpressions.getMyChildren(pn:132)
at com.adbs.ast.AstNodeBase.dispose(wc:98)
at com.adbs.ast.AstNode.dispose(nc:86)
at com.adbs.querybuilder.QueryBase.loadFromAST(fm:80)
at com.adbs.querybuilder.UnionGroup.loadFromAST(uh:1411)
at com.adbs.querybuilder.SubQuery.loadFromAST(zo:351)
at com.adbs.querybuilder.Query.loadFromAST(xf:30)
at com.adbs.querybuilder.QueryBuilder.e(uj:2579)
at com.adbs.querybuilder.QueryBuilder.e(uj:1347)
at com.adbs.querybuilder.QueryBuilder.setSQL(uj:1134)
at oracle.dbtools.raptor.controls.query.QueryBuilderEditPanel$6.construct(QueryBuilderEditPanel.java:636)
at oracle.dbtools.raptor.utils.NamedSwingWorker$2.run(NamedSwingWorker.java:115)
at java.lang.Thread.run(Thread.java:619)

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Please note that I didn't click on the "Query Builder" tab, neither do I want to use the Query Builder at all. I can just close the message and get back to work, but the dialogue is annoying. Is there any way to stop it? Disabling Query Builder would be an option, but I couldn't find anything relevant in Preferences.

I'm using SQL Developer 3.0.04.