incorrect base64 write/read with expo-file-system?

Here is a reproducible code: https://gist.github.com/somidad/1c347b650039a1a140baf6f232683bbe

Based on the result, what I understand is that:

• If the length is multiple of 4, writing succeeds and reading correctly recovers the original string
• Else if the length modulo 4 is equal to 1, writing raises an error
• Else if the length modulo 4 is equal to 2 or 3, writing and reading did work, but the last character gets corrupted (and padding follows)

Is it expected behavior? Or am I missing something to get it to work as expected?

For those who may not want to visit my gist, I copied and pasted it below:

Code

import {
  documentDirectory,
  readAsStringAsync,
  writeAsStringAsync,
} from "expo-file-system";
import { Button, View } from "react-native";

export default function Temp() {
  async function temp(s: string) {
    try {
      await writeAsStringAsync(documentDirectory + "temp.txt", s, {});
      await writeAsStringAsync(documentDirectory + "temp.bin", s, {
        encoding: "base64",
      });
      const t2t = await readAsStringAsync(documentDirectory + "temp.txt", {});
      const b2b = await readAsStringAsync(documentDirectory + "temp.bin", {
        encoding: "base64",
      });
      console.log("Original".padEnd(48, " "), s);
      console.log("  Write as text, read as text:".padEnd(48, " "), t2t);
      console.log("  Write as base64, read as base64:".padEnd(48, " "), b2b);
    } catch (error) {
      console.error(error);
    }
  }

  return (
    <View style={{ padding: 8 }}>
      <Button
        title="Temp"
        onPress={async () => {
          console.log("Test");
          const s = "0123456789abcdef";
          for (let i = 1; i <= s.length; i++) {
            await temp(s.substring(0, i));
          }
          console.log("========");
        }}
      />
    </View>
  );
}

Result (log)

 (NOBRIDGE) LOG  Test
 (NOBRIDGE) ERROR  [Error: Call to function 'ExponentFileSystem.writeAsStringAsync' has been rejected.
→ Caused by: java.lang.IllegalArgumentException: bad base-64]
 (NOBRIDGE) LOG  Original                                         01
 (NOBRIDGE) LOG    Write as text, read as text:                   01
 (NOBRIDGE) LOG    Write as base64, read as base64:               0w==
 (NOBRIDGE) LOG  Original                                         012
 (NOBRIDGE) LOG    Write as text, read as text:                   012
 (NOBRIDGE) LOG    Write as base64, read as base64:               010=
 (NOBRIDGE) LOG  Original                                         0123
 (NOBRIDGE) LOG    Write as text, read as text:                   0123
 (NOBRIDGE) LOG    Write as base64, read as base64:               0123
(Omitted logs showing the same pattern)