QuestaSim "Trace back: can't read..." error popup in gui mode

When using "--gui" and QuestaSim-64 10.6a in mode, just after adding all the waveforms to the wave window, this arcane error pops up in a window that you have to click away before it continues with simulation.

The trace of the error:

```
# Trace back: can't read "tbX(tbf21)": no such element in array
# while executing
# "lappend orderx($tbX($tb)) $tb"
# (object "::.dockbar" method "::mtiwidgets::Dockbar::redoPack" body line 34)
# invoked from within
# "redoPack again"
# ("eval" body line 1)
# invoked from within
# "eval $args"
# (object "::.dockbar" method "::mtiwidgets::Dockbar::_delayedEval" body line 3)
# invoked from within
# "::.dockbar _delayedEval redoPack again"
# (in namespace inscope "::mtiwidgets::Dockbar" script line 1)
# invoked from within
# "namespace inscope ::mtiwidgets::Dockbar ::.dockbar _delayedEval redoPack again"
# ("after" script)
# <2:/opt/applics/questasim-10.6a/questasim/linux_x86_64/tk8.6/bgerror.tcl:106: ::tkerror {can't read "tbX(tbf21)": no such element in array}
# <1:eval:1: ::tk::dialog::error::bgerror {can't read "tbX(tbf21)": no such element in array}
```