I have been facing this problem (using the -raw option with the get-property command) more than once and in different situations.
Here is the error produced in the details of the failure:
I haven't traced all the different styles that produced that error but here is the portion of the script that caused that error:
The only items that the -raw option works well with are the simple tree items or so.
Please have a look at that issue.
|Field||Original Value||New Value|
|Remaining Estimate||2 hours [ 7200 ]|
|Original Estimate||2 hours [ 7200 ]|
|Fix Version/s||1.2.15 [ 11972 ]|
|Fix Version/s||1.2.16 [ 11974 ]|
|Transition||Time In Source Status||Execution Times||Last Executer||Last Execution Date|
|6d 23h 41m||1||sergey||21/Jan/13 8:04 PM|