Hi,
I am submitting a case for this as well on monday. I have prepared a 6 page document with screenshots for this one :)
It is not only the two date fields, but also the book depreciation field which gets cleared if you use default CMDB values.
Also this behaviour seems to be occuring after setting a value which triggers a popup or drop downlist, such as filling in the manufacturer/model fields or setting cost center ownership.
Even more, if you set default values for the book depreciation field and then lookup the manufacturer or model it gets cleared. If you then want to select the book depreciation again it not only gives you a popup to select a depreciation schedule, but also a whole new asset popup comes on top of that!
btw, I have reproduced this in three diferrent and clean ITMS 7.1 SP2 environments. So I suppose it is definitely a bug.
kr,
dawi_x