User-Agent:       Mozilla/5.0 (Windows NT 6.1; WOW64; rv:11.0) Gecko/20100101 Firefox/11.0
Build Identifier: 

The reference to a vector generated by a plugin is lost after saving.  This only happens if the plugin is created after the equation and then the equation is edited to include a reference to the plugin vector.

Reproducible: Always

Steps to Reproduce:
1. Use Create > Vector to generate a vector called "INDEX" with say 100 points from 0..99 
2.Use Create > Equation to create an equation called "EQ1" to simulate raw data (e.g. SIN(x) with INDEX as the x-vector)
3. Create another equation "EQ2" that manipulates the raw data (e.g. 2*[EQ1:y]) 
3.Use Create > Filter Plugin > Despike to generate a new vector based on the simulated raw data (EQ1:y)
4. Now go back and edit the equation EQ2 to reference the despiked data instread of the raw data (i.e. 2*[EQ2:y])
5. Save the kst file, close and reopen.
6. Open the data manager to read the contents of EQ2. The reference to the plugin vector will be missing.
Actual Results:  
The equation loses its reference to the plugin vector after reopening the file.

Expected Results:  
The equation should not lose its reference to the plugin vector after closing and reopening the file. If an equation can not reference a vector created after itself then the user should be prevented from doing so.