Found in 3.6 rc1, I was changing all my tab 
values from 4 to 3 and it didn't save them. After 
entering a value, you must hit tab to make the 
new value stick.

Repo:
1)Tools, Options, Editing, Indentation Engines
2) Select the first engine, change "Number of 
spaces per tab" from 3 to 4.
3) Select next engine, then click back to first 
engine and note the numerical value is not saved.
4) To make it save, must hit tab to allow control 
to notice the value has changed. You can't even 
mouse to the previous value "Expand Tabs to 
Spaces" to make the value save.