controls can become unresponsive in certain situations

[yourhead]

to repeat:

• select on a stack
• click on a disclosure triangle to "close" a group -- the group must have been open initially when the stack was selected
• click on the same triangle to "open" the group
• modify a control within the the group

the result is that the control is unresponsive.

[yourhead]

fixed in 3.5.7 beta 3