Why -right click contextual menu to 'look up' a word (in Apple's dictionary) issues intermittently.

Can any one tell why, when using the right click contextual menu to 'look up' a word in Apple's dictionary—within text, that after a while it highlights the right word but actualy looks up an assortment of letters containing only a portion of the acutal word. Doesn't always happen only Intermittently...usally stops with a restart...but that is damned inconvenient. I hate that I can't rely on this wonderful resource. Most often is an issue in iText and like minded wordprocessors ie BEAN ( a wonderful simple powerful upscale version of iTEXT type, wordprocessor. . I can't live without BEAN for my wriiting and research... HELP, Please. Thanks