Tx Andrei for looking into this problem.
Yes, my example works with your fix and the rows heights are computed correctly.
However, when we do not provide the size for the last row, it appears that row size exceeds the container (column) size (height). So, to reproduce you need to remove the size of the third pane to see the problem:
|tab|
tab := GLMTabulator new.
tab column: [ :col |
col
row: #first size: 80;
row: #second;
row: #third ].
tab transmit to: #first; andShow: [:a | a dropDownList display: [:x | 1 to: x ] ].
tab transmit to: #second; andShow: [:a | a list display: [:x | 1 to: x ] ].tab transmit to: #third; andShow: [:a | a list display: [:x | 1 to: x ] ].
tab openOn: 10
usman