Transfer logging,trace levels from old to new global loggers.

main/command/src/main/scala/sbt/MainLoop.scala

@@ -65,9 +65,22 @@ object MainLoop
 	def runWithNewLog(state: State, logBacking: GlobalLogBacking): RunNext =
 		Using.fileWriter(append = true)(logBacking.file) { writer =>
 			val out = new java.io.PrintWriter(writer)
-			val loggedState = state.copy(globalLogging = state.globalLogging.newLogger(out, logBacking))
+			val newLogging = state.globalLogging.newLogger(out, logBacking)
+			transferLevels(state, newLogging)
+			val loggedState = state.copy(globalLogging = newLogging)
 			try run(loggedState) finally out.close()
 		}
+
+	/** Transfers logging and trace levels from the old global loggers to the new ones. */
+	private[this] def transferLevels(state: State, logging: GlobalLogging) {
+		val old = state.globalLogging
+		Logger.transferLevels(old.backed, logging.backed)
+		(old.full, logging.full) match { // well, this is a hack
+			case (oldLog: AbstractLogger, newLog: AbstractLogger) => Logger.transferLevels(oldLog, newLog)
+			case _ => ()
+		}
+	}
+
 	sealed trait RunNext
 	final class ClearGlobalLog(val state: State) extends RunNext
 	final class KeepGlobalLog(val state: State) extends RunNext

util/log/src/main/scala/sbt/Logger.scala

@@ -40,6 +40,11 @@ abstract class AbstractLogger extends Logger
 
 object Logger
 {
+	def transferLevels(oldLog: AbstractLogger, newLog: AbstractLogger) {
+		newLog.setLevel(oldLog.getLevel)
+		newLog.setTrace(oldLog.getTrace)
+	}
+
 	// make public in 0.13
 	private[sbt] val Null: AbstractLogger = new AbstractLogger {
 		def getLevel: Level.Value = Level.Error