peculiar behavior of logger.rb under Rails

I am using logger to record method calls in a Rails app. It is used in the context of some "set_trace_func proc" code, which is invoked at the start of ".../public/dispatch.fcgi".

As the app runs, a log of all method calls is generated. However, at line 5463 in the log, the line prefixes go away:

  I, [09:44:43#26539] INFO -- : call 8 Object:method_added ...   I, [09:44:43#26539] INFO -- : call 8 Object:method_added ...   call 8 Object:method_added ... (P07/blankslate.rb:57)   call 7 Kernel:require ... (P04/custom_require.rb:26)

The prefixes do not reappear in the remainder of the (26979 line) log. To eliminate the possibility that logger gets confused at a given number of output lines, I wrote a simple test script:

  #!/usr/bin/env ruby

  require '/usr/local/lib/ruby/site_ruby/1.8/boswell.rb'   Boswell.new('/tmp/rdm/TST')

  def foo     a=1   end

  50000.times do     foo   end

However, this did not reproduce the problem. So, I assume that there is some untoward interaction going on with the Rails code. Can anyone suggest a way of tracking this down?

-r