displaying the current position in waveform: problems with long samples

i'm trying to visualize the waveform and the current playing position in the performance view.
i more or less accomlpished what i needed but i found an odd behaviour with long samples

i'm using the examples from the manual:

on init
declare $play_pos
declare ui_waveform $Waveform(6,6)
attach_zone ($Waveform,find_zone ("Test"),0)
end on

on note
while ($NOTE_HELD = 1)
$play_pos := get_event_par($EVENT_ID,$EVENT_PAR_PLAY_POS)
set_ui_wf_property($Waveform,$UI_WF_PROP_PLAY_CURSOR,0,$play_pos)
wait (10000)
end while
end on

if the sample is "too long" (e.g. i have 8 bar loops), i notice that $play_pos variables exceed a maximum value (don't know how much...) and the player bar does not reach sample end. Even if the sample is correctly playing, on the waveform display the player bar reset to the sample start and the "current position" displayed is lost.

is it a bug? do i miss something? is there a workaround?