Yeah, the first time I actually tested it (at first I didn't notice) I had ~1.5s/attack. After 5 common upgrades with 3 tomes I still had ~1.5s/attack. It should have been 37.5% faster for each at that point, which should have dropped it to about 0.14s/attack. And as soon as I got the uncommon one it went to ~1.1s/attack
Edit: Just to confirm for you, the 2.3 patch does not appear to have changed this bug. 0-1 tome still operates as it should, 2+ tomes cause common attack speed upgrades to have no effect, uncommon versions still work properly.
I did not expect it to have changed, just thought I should let you know after the patch as I am aware of how strangely code can behave sometimes...