[Paraview] Plugin crashes if source filter is not applied

[redkite]

Hi,

On function of my plugin operates on some point data on the surface of 
my model to create a new filter. This works well enough if the user 
selects points, uses the 'Extract Selection Filter' and remembers to 
click Apply.

I can check if the active source filter is an 'ExtractSelection' easily 
enough by name, which is some help, but if the user has not clicked 
apply, ParaView likes to crash out (PV 4.1 on Windows 7 does anyway). 
Auto-apply is better avoided, especially for large models.

Is there a way to check to check if the source data has (or has not) 
been extracted and applied?

I've tried using UpdateVTKObjects() etc to force the apply, but no joy...

regards,
Richard