Ambidextrous - intentional or bug? No "max 20" on the +1 to DEX.

Unlike the other feats, the Ambidextrous feat simply says "+1 DEX".  There is no warning about "max 20".

However, if you take this feat on a character that already has a 20 DEX, the +1 is not applied at your DEX stays at 20.

I presume the bug is the missing warning and not that DEX should have gone to 21.