PR# 4145 Calling current_line_number from caret_moved call back in rich text sometimes causes post condition

I have a rich text widget in which I have registered a call back when the caret moves. From this call back I call current_line_number. Sometimes when the cursor moves the post condition in current_line_number fails:

valid_line_index: valid_line_index (Result)

Call stack:

   ObjectClassRoutine
   ------------------
:: [0xF65535C0] TEXT_EDITOR current_line_number (From EV_TEXT) ( @ 3 )
-> [0xF65535C0] TEXT_EDITOR caret_moved ( @ 3 )
:: [0xF65535BC] PROCEDURE rout_obj_call_procedure ( @ 0 )
:: [0xF65535BC] PROCEDURE apply ( @ 3 )
:: [0xF65535BC] PROCEDURE call (From ROUTINE) ( @ 4 )
:: [0xF65535B8] EV_INTEGER_ACTION_SEQUENCE call (From ACTION_SEQUENCE) ( @ 12 )
:: [0xF65535B4] EV_RICH_TEXT_IMP on_text_mark_changed ( @ 11 )
:: [0xF65535B0] EV_GTK_CALLBACK_MARSHAL text_buffer_mark_set_intermediary (From EV_GTK_DEPENDENT_INTERMEDIARY_ROUTINES) ( @ 5 )
:: [0xF65535AC] PROCEDURE rout_obj_call_procedure ( @ 0 )
:: [0xF65535AC] PROCEDURE apply ( @ 3 )
:: [0xF65535AC] PROCEDURE call (From ROUTINE) ( @ 4 )
:: [0xF65535B0] EV_GTK_CALLBACK_MARSHAL translate_and_call ( @ 7 )
:: [0xF65535A8] PROCEDURE rout_obj_call_procedure ( @ 0 )
:: [0xF65535A8] PROCEDURE apply ( @ 3 )
:: [0xF65535A8] PROCEDURE call (From ROUTINE) ( @ 4 )
:: [0xF65535B0] EV_GTK_CALLBACK_MARSHAL marshal ( @ 10 )
:: [0xF65535A4] EV_APPLICATION_IMP g_main_iteration (From EV_GTK_EXTERNALS) ( @ 0 )
:: [0xF65535A4] EV_APPLICATION_IMP main_loop ( @ 13 )
:: [0xF65535A4] EV_APPLICATION_IMP launch ( @ 2 )
:: [0xF65535A0] RADICAL_IDE launch (From EV_APPLICATION) ( @ 4 )
:: [0xF65535A0] RADICAL_IDE make ( @ 6 )