Narrative:

I was cleared from FL210 to 16000' 10 NM northeast of jax. At 16000' ZJX cleared me to 12000', pilot's discretion, and cross 35 NM north of jax at 10000'. I planned my descent to cross 35 NM north at 10000'. As I passed through 11600' the controller asked my altitude. I reported 11500'. He said my altitude was supposed to be 12000'. He said the clearance was 'to expect' 10000' 35 north of jax. I did not hear a readback of the 'to expect' part of the clearance. I leveled at 12000'. The controller then reported small aircraft traffic at 11000' northbound, 4 mi off my left wing. I had not been given any traffic prior to his question as to what my altitude was. I never saw the traffic and the flight continued to jax. Landed and called the FSS at jax.

Related reports:

Google
 

Original NASA ASRS Text

Title: PLT OF LIGHT TWIN ENGINE ACFT MISUNDERSTANDS CLRNC AND OVERSHOOTS ASSIGNED ALT ON DESCENT.

Narrative: I WAS CLRED FROM FL210 TO 16000' 10 NM NE OF JAX. AT 16000' ZJX CLRED ME TO 12000', PLT'S DISCRETION, AND CROSS 35 NM N OF JAX AT 10000'. I PLANNED MY DSCNT TO CROSS 35 NM N AT 10000'. AS I PASSED THROUGH 11600' THE CTLR ASKED MY ALT. I RPTED 11500'. HE SAID MY ALT WAS SUPPOSED TO BE 12000'. HE SAID THE CLRNC WAS 'TO EXPECT' 10000' 35 N OF JAX. I DID NOT HEAR A READBACK OF THE 'TO EXPECT' PART OF THE CLRNC. I LEVELED AT 12000'. THE CTLR THEN RPTED SMA TFC AT 11000' NBND, 4 MI OFF MY LEFT WING. I HAD NOT BEEN GIVEN ANY TFC PRIOR TO HIS QUESTION AS TO WHAT MY ALT WAS. I NEVER SAW THE TFC AND THE FLT CONTINUED TO JAX. LANDED AND CALLED THE FSS AT JAX.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.