Dotted duplets in compound time (0.9.6 regression)

To reproduce this bug:
1. Create a new score in 12/8 time
2. Select a dotted quarter note
3. Hit Ctrl+2 to make a duplet
4. Enter some notes

Behavior:
The default selected note will be a dotted 8th. Two of these will fit into the duplet. When a plain 8th note is selected instead, three fit into the duplet.

Expected behavior:
There should be plain 8th notes instead of dotted 8ths in the duplet.