Picture capture time increases during test

I have to resort to text recognition to identify codejock tabs. To find the active tab I then need to test that the background colour of the text object is blue. The picture capture takes about 1 second at the start of the test run but grows exponentially. After I have opened and identified about 50 forms it can take 5 seconds just to capture the picture object. I have seen it take 19 seconds on several runs. This can add up to 15 minutes to each test run.

Any ideas why capturing a picture object may take an increasing amount of time? Do I need to flush something periodically?

VBScript:

function isFormCurrent(form)
'Tests if the form named has the correct background colour that indicates it is the current form
  isFormCurrent = false
  if len(form)>0 then
    if project.Variables.OpenForms.exists then
      sys.refresh
      set textObj = project.Variables.OpenForms.waitchild("TextObject(""" & form & "*", 0)     
      if textObj.exists then
        'Test if the form is current by inspecting the top left pixel of the tab label against the current form BG colour
        set TabPic = textObj.picture 'THIS IS THE COMMAND THAT TAKES INCREASING TIME TO EXECUTE
        pixColour = TabPic.Pixels(0,0)

        if pixColour = CurrentFormBGColour then
          isFormCurrent = true
        end if
      end if
    end if
  end if
end function

I used the above code and made it verbose so that I could surround each line with the following to identify which step was causing the increasing delay each time I opened a new form.

startTime = aqDateTime.Time()
...
log.error("DEBUG: isFormCurrent took " & aqConvert.TimeIntervalToStr(aqDateTime.TimeInterval(startTime, aqDateTime.Time()) ) & " to execute step" )

Thanks,