The scripthelper addon function ExecuteString doesn't handle context reference counting properly if Prepare returns an error code.

Instead of returning contexts retrieved using asIScriptEngine::RequestContext, it calls release:

// If no context was provided, request a new one from the engine
asIScriptContext *execCtx = ctx ? ctx : engine->RequestContext();
r = execCtx->Prepare(func);
if( r < 0 )
{
	func->Release();
	if( !ctx ) execCtx->Release();
	return r;
}

Normal execution will handle this correctly:

if( !ctx ) engine->ReturnContext(execCtx);

it should use the latter method in both cases.