Unexpected inconsistency with some custom dictionary words prefixed with "a "

[wesbiggs]

yaspeller exhibits some strange behaviour in some circumstances when checking certain words prefixed with the word "a".

It can be reproduced using the command line invocation.

Setup:

mkdir yaspeller-issue; cd yaspeller-issue
npm init -y
npm i yaspeller
echo '{"dictionary":["blockchain"]}' > .yaspellerrc.json

Test cases:

The word by itself is correctly allowed.

echo "blockchain" | ./node_modules/.bin/yaspeller --stdin -l en
Spelling check:
✓ stdin 379 ms
No errors.
Checking finished: 0.477 sec.

The word prefixed by "a " causes an error.

echo "a blockchain" | ./node_modules/.bin/yaspeller --stdin -l en
Spelling check:
✗ stdin 378 ms
-----
Typos: 1
1. a blockchain (1:1, suggest: black chain)
-----

Fix typo or add word to dictionary at .yaspellerrc.json ("dictionary" property) if you are sure about spelling. Docs: https://github.com/hcodes/yaspeller#configuration
Checking finished: 0.48 sec.

"on a blockchain" is fine.

echo "on a blockchain" | ./node_modules/.bin/yaspeller --stdin -l en
Spelling check:
✓ stdin 375 ms
No errors.
Checking finished: 0.474 sec.

But "by a blockchain" is not.

echo "by a blockchain" | ./node_modules/.bin/yaspeller --stdin -l en
Spelling check:
✗ stdin 374 ms
-----
Typos: 1
1. a blockchain (1:4, suggest: black chain)
-----

Fix typo or add word to dictionary at .yaspellerrc.json ("dictionary" property) if you are sure about spelling. Docs: https://github.com/hcodes/yaspeller#configuration
Checking finished: 0.472 sec.

Tested against version 8.0.1.

Other words that are known to trigger the error in similar circumstances are "blockchains" and "mainnet". However, "mainnets" is OK.