This issue is found in Cisco IP Communicator version 1.1(2) and earlier, in which the speakerphone causes the Dual-tone Multifrequency (DTMF) tones to be played in-band, in addition to the out-of-band DTMF provided by Cisco CallManager.
No issues are observed when the same calls are made with an IP phone.
For earlier Cisco IP Communicator versions, this issue is addressed in Cisco bug ID CSCee61075.
The workaround provided is to Mute the call when the DTMF tones must be entered, or to use an actual headset. This way, the DTMF tones played to the user are not also received by the microphone.
In versions 1.1(3) and later, the DTMF tones are not played when the Cisco IP Communicator Speakerphone button is used.
This issue can still occur if the user has the Headset button selected, but is not actually using a Headset. To resolve this, the user may either use the Speaker button instead, or choose to Mute the call when entering DTMF digits.