Hmm.. I did not try to cancel out of the card creation, but I could possibly have tabbed back to the browser too quickly(?) while the console that appears for half a second when creating cards appeared.

When making a new card it made 2 duplicate cards with messed up syntax.
The bug only happened one instance while mining. Then the extension goes back to working as expected.
I've only encountered the same bug once before, a few months ago.
I was not able to replicate the bug.

From the Meaning field:
"かた[,かたい;h] {[;a] ‐}て { }【片手[かたて;h,o] [かた[;a] て {;h,o] }】{{ ★★★★
① }}一方[いっぽう;n3] [いっぽう[;n3] {;n3] }の { }手[しゅ] [て {;o] }。「―で { }持[も;o]ち 上[じょう;a] [もち[;a] あ ,もちあげる ;h,k4]げ る { }」
⇔両手[りょうて;h] [りょう て {;h] (1)：}両手[りょうて;h] [りょう て {;h] {(2)
② }}一方[いっぽう;n3] [いっぽう[;n3] {;n3] }。「舞台[ぶたい;a] [ぶた[;h] い[,いる;h] {;a] }の { ―}」{{
③ }}片手間[かたてま;h,o] [かた[;a] て ま {;h,o] }。「―仕事[しごと;h] [し[,する;h] ごと[;h] {;h] }」{{
④ ｟}}俗[ぞく;h] [ぞ く {;h] ｠（}五[ご;o] [ご {;o] }本[ほん;a] [ほん[;a] {;a] }の { }指[ゆび;o] [ゆ び{;o] }から[;a] {[;a] ）}五[ご;o] [ご {;o] ○[}れい {] ○[}れい {] ○[}れい {] }円[えん;a] [えん[;a] {;a] }、五[ご;o] [ご {;o] }万[まん;a] [ま ん {;a] }円[えん;a] [えん[;a] {;a] }など[;a] {[;a] }五[ご;o] [ご {;o] }の { }つく[,つく;k1] [,つく[,つく;k1] {;k1] }金額[きんがく;h] [きん がく[;a,o] {;h] }を { }いう[,いう;o] [,いう[,いう;o] {;o] }語[ご;o] [か たり {] }。"

When attempting to remove syntax with f4 from the word field this remains:

From the Meaning field:
かたて;h,o] 】 ★★★★
① 一方;n3] の 手ち上あ,もちあげる;h,k4]げる 」
⇔両手(2)
② 一方;n3] 。「舞台い;a] の ―」
③ 片手間てま;h,o] 。「―仕事ごと;h] 」
④ ｟俗;a] の 指;a] 、五;a] など;k1] 金額;h] を いう;o] 語[かたり] 。

Hope this report is in anyway helpful