Lost synchronization between VIVA calculator and schematic

Hi everybody,

I am using cadence IC6.1.5.64b.500.17 with MMSIM 13.10.087.

I face a recurrent issue when using my calculator to pull signal from schematic to the expression editor. 

After a simulation performed in either ADEL or ADEXL, I open the calculator. I do it either from ADEL->Tools->Calculator or from ADEXL>Tools>Calculator.

Then I press the VT tick button  (for instance) and try to pick up a net in my schematic (which is automatically opened by doing so if it wasn't previously). At the beginning this works fine and the desired signal appears in the expression editor (for instance VT("/vdd")).

But after some time and many simulations (I could not determine the triggering event), clicking on a net within the schematic simply does select it, not pulling anything within the expresison editor of the calculator anymore. I can still read "Select the nets for VT expression" in the bottom bar of the schematic window, but that's all.

Manually typing the desired expression will work fine and the plot will be correct, corresponding to the simulation I did perform,  but it's completely impossible to get it automatically as usual.

Restarting virtuoso I can get my expression editor working fine again.

Does anybody face this issue and knows how to fix it?

Many thanks!

Thibault