impress animation: Grow and Shrink not working as expected

Here is how you can reproduce this:

Draw an object (a simple rectangle will suffice). Animate it with Grow and Shrink - 50% and then again Grow and Shrink 100%. The expected behavior was for the object to shrink tho half of its size then go back to the original size. But it goes back to a larger size for some reason. For the 2nd part (Grow) I tried other combinations, for example: 101% is a lot bigger than the original size and 99% is smaller than the 50% (which I assume is 99% of the 50% size).

So, how do I get this behavior of shrinking to half of a size and going back to the original one?
I attached a gif showing what I mean.

C:\fakepath\impress-issue(1).gif

The UI is still buggy, see https://bugs.documentfoundation.org/show_bug.cgi?id=108450. You can try to set values directly in the file. But that needs some XML and SMIL knowledge. The files attached to the issue might help so see, what needs to be written. So there exists currently no way for ordinary users to set specific values besides those given in the UI.