Most often I notice this with katakana, where a small tsu (intended to indicate the following consonant is "long", or geminated for a more linguistic term) is pronounced as if it were a large one (which actually does in fact make the sound 'tsu'). I can't remember all the instances in which I've seen this happen, but most recently I had this happen with seemingly 100% consistency with Emily on the word ドッグ in the sentence "わしは… イタコ・ドッグじゃ。" and it'd happen if I rewrote it in hiragana instead.