Undo command is not available after suppressing assembly components

Issue

When you suppress some components in an Inventor assembly, you notice that the UNDO button is grayed out. However this does not happen every time and not for all assembly components.
Here is the background on why this happens.

Solution

The UNDO command may become unavailable after the suppression of a component because Inventor unloads the component from memory once there are no other occurrences of this particular component present in the assembly. 
As long as there are other occurrences of the component, suppression will not disable the UNDO command.

There are 2 possible scenarios:

1. The assembly contains a single occrurence of different parts (for example 1x Part1, 1x Part2 and 1x Part3).
   When you suppress any of these parts, Inventor unloads it from memory because the assembly contains only one occurrence of the part. The result is that the UNDO command will not be available.
2. The assembly contains several occurrences of the same part (for example 3x Part1, 1x Part2 and 2x Part3). When you suppress one of the occurrences of Part1 or Part3, Inventor doesn’t unload these parts from memory because other occurrences of these parts are still present in the assembly. The result is that the UNDO command remains available.

The next video demonstrates the logic of UNDO command after suppressing components: