CRJ200 HAS STABILIZER TRIM MALFUNCTION DURING APCH AND LNDG AT CVG.

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WE WERE ON A VISUAL APCH TO RWY 18R IN CVG IN SEVERE CLR WX. IT WAS MY LEG. I DISCONNECTED THE AUTOPLT AT ABOUT 4 MI; APPROX OVER OR BEFORE REACHING THE OHIO RIVER. I TRIMMED THE ACFT UP AND TO MY KNOWLEDGE DID NOT TOUCH THE TRIM AGAIN FOR THE REST OF THE APCH; AS I ALWAYS DO ON SUCH APCHS. UPON ENTERING THE FLARE OR SLIGHTLY BEFORE IT; THE CLACKER FOR THE TRIM SOUNDED; SIGNIFYING A TRIM INPUT (I BELIEVE IT SHOULD SOUND ONLY IF THE INPUT IS FOR MORE THAN 3 SECONDS). I LOOKED AT THE TRIM INDICATION AND SAW IT WAS INCREASING. MY FINGER WAS NOT ON THE TRIM SWITCH. SINCE WE WERE IN THE FLARE I THOUGHT IT PRUDENT TO SIMPLY LAND. BEFORE WE TOUCHED DOWN THE TRIM STOPPED AT A SETTING OF 8.4. UPON TAXIING IN I TOLD THE CAPT THAT I DID NOT TRIM THE ACFT DURING THE FLARE. HE THOUGHT IT PRUDENT; AND I AGREED; TO WRITE UP THE EVENT IN THE MAINT LOG. AS STATED BEFORE I AM NOT IN THE HABIT OF TRIMMING DURING THE FLARE. IS IT WITHIN THE REALM OF POSSIBILITY THAT I HIT THE TRIM SWITCH? POSSIBLY; BUT I HAVE NEVER HAD THE TRIM SETTING UP AT 8.4 BEFORE; INTENTIONALLY OR OTHERWISE AND DON'T KNOW ANYONE ELSE WHO DOES EITHER. THE CAPT AND I HAD 10 OTHER LEGS ON THAT TRIP ON OTHER ACFT AND NEVER HAD THAT HAPPEN ON ANY OF THEM. BEING IN THE FLARE WHEN IT HAPPENED IT SEEMED SAFER TO LAND THE ACFT RATHER THAN TRY TO REJECT THE LNDG WITH A POSSIBLE PITCH TRIM RUNAWAY. IF THERE WERE A SPECIFIC SETTING WE WERE TAUGHT TO SET FOR PITCH TRIM ON LNDG; PERHAPS I WOULD HAVE BEEN MORE AWARE IF I OR THE AIRPLANE WERE GIVING INPUTS THAT WERE DEVIATING FROM THAT SETTING.