[Maybe bug] False Positive of vosk-android-demo while I shut up

I'm trying to build a single syllable voice keyboard (without using the NATO phonetic alphabet) to speed up keystroke typing and to accurately input variable abbreviations.

I know chinese characters are all of single syllable, so I make a prototype verification based on vosk-android-demo(https://github.com/alphacep/vosk-android-demo):

I replaced the models/assets/model-en-us in vosk-android-demo with models/assets/vosk-model-small-cn-0.3,
modified app/java/org.vosk.demo/VoskActivity.java:
```
StorageService.unpack(this, "vosk-model-small-cn-0.3", "model", .....

Recognizer rec = new Recognizer(model, 16000.0f, "[\"诶\", \"逼\", \"西\", \"第\", \"依\", \"飞\", \"鸡\", \"黑\", \"挨\", \"接\", \"尅\", \"勒\", \"摸\", \"你\", \"欧\", \"批\", \"哭\", \"啊\", \"斯 [unk]\", \"踢\", \"优\", \"微\", \"乌\", \"叉\", \"歪\", \"热\", \"[unk]\"]");
```
The 26 chinese characters match the 26 english letters.

Compiled and installed the apk into my phone, click "Recognize Microphone", it shows:
```
{"partial": ""}
{"partial": ""}
{"partial": ""}
{"partial": ""}
.....
```

Then I begin to speak, the result is amazing,
it's far more accurate and quicker than "pocketsphinx / google SpeechRecognizer(EXTRA_PREFER_OFFLINE) / tensorflow lite(teachable machine)",
when I say 诶(ey), 逼(bee), 西(shee), 第(dee), 依(yee), 飞(fey), ....,
every chinese chracter will show correctly in the app.

But after I shut up, it continue scrolling to show:
```
{"partial": "飞"}
{"partial": "你"}
{"partial": "飞"}
{"partial": "你"}
.....
```

I think it should show "{"partial": ""}" while no human voice detected, maybe it's a bug.

And I don't want use the chinese model to recognize 26 letters, but I can't figure out the detail steps to retrain a single syllable phonetic dictionary of only 26 letters, anyone give me a hint:
```
a EY
b B EE
c S EE
d D EE
e EE
f F EY
g JH EE
h HH EY
.....
```