Copy/Pasting CustomHLSL Blocks erase they slots values

Steps to reproduce:

1. Open a VFX
2. Create a CustomHLSL Block. 
3. Change the default value of the offset or speed factor.
4. Select and copy the HLSL block.
5. Paste the block in the same context or elsewhere.

Actual results: The values are not preserved after pasting and are reset to zero.

Expected results: The values of the slots should be maintained between the original and the copy.

Reproducible with versions: 6000.3.0b1