Narrative:

During descent to 7000 ft controller gave a speed reduction from 250 KTS to 180 KTS. MD88 has IAS mode that works fine, but system has this anomaly. If in 'altitude capture' mode, any adjustment to flight control panel will cancel altitude capture. I did not notice altitude capture when speed adjustment was made because FMA is in a different place than flight control panel. I knew that, but it got me anyway. Aircraft did not capture 7000 ft, and we descended to about 6700 ft before climb was established. After returning to 7000 ft, we were given 5000 ft almost immediately. There were no conflicts that I am aware of.

Google
 

Original NASA ASRS Text

Title: MD88 CREW HAD AN ALT OVERSHOOT IN CVG CLASS B AIRSPACE.

Narrative: DURING DSCNT TO 7000 FT CTLR GAVE A SPD REDUCTION FROM 250 KTS TO 180 KTS. MD88 HAS IAS MODE THAT WORKS FINE, BUT SYS HAS THIS ANOMALY. IF IN 'ALT CAPTURE' MODE, ANY ADJUSTMENT TO FLT CTL PANEL WILL CANCEL ALT CAPTURE. I DID NOT NOTICE ALT CAPTURE WHEN SPD ADJUSTMENT WAS MADE BECAUSE FMA IS IN A DIFFERENT PLACE THAN FLT CTL PANEL. I KNEW THAT, BUT IT GOT ME ANYWAY. ACFT DID NOT CAPTURE 7000 FT, AND WE DSNDED TO ABOUT 6700 FT BEFORE CLB WAS ESTABLISHED. AFTER RETURNING TO 7000 FT, WE WERE GIVEN 5000 FT ALMOST IMMEDIATELY. THERE WERE NO CONFLICTS THAT I AM AWARE OF.

Data retrieved from NASA's ASRS site as of July 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.