Worked: ??? at least >= 2.62 behaves this way
Description of error
When the particle type is set to hair, keyed values cannot be changed. While a keyed value can be edited, it snaps back to the keyed value when you finish editing, preventing you from entering a second value to key or replacing an existing keyed value. This is only in the particles UI as changes can be made within the graph editor.
Some values can be changed, eg within the Rendered and Display panels. Of note is that any keyed values that can be altered will all snap back if an un-alterable value is edited.
It would appear to be like a frame change or scene update is being triggered after editing values.
Exact steps for others to reproduce the error
- add a particle system to an object and change the type to hair.
- keyframe a value
- try and change the value