Crash when saving edited Unown in Gen 2 with unhandled exception

[BeyondTheHorizon]

Hi, I'm currently going through GSC Smogon sets and got to Unown. Yeah, Unown. When I tried saving the following Unown file, PKHeX crashed with an unhandled exception. Since I can't upload the .pkm file because of this, I'll provide you the information in text.

Species: Unown

Nickname: None

Level: 100

Held Item: TwistedSpoon

Friendship: 255

Form: X

Language: ENG (English)

Is Egg: No

Infected: No

Cured: No

Met: Ruins of Alph

Met Level: 5

Time of Day: Day

IV Stats: 11 HP IVs / 15 Atk IVs / 12 Def IVs / 15 SpA IVs / 15 SpD IVs / 15 Spe IVs

EV Stats: 65535 EVs on all Stats

Attacks: Hidden Power (Psychic)

TID: 65535

OT: GOLD

[Kaphotics]

Unable to replicate.

201-23 - UNOWN - F3BB.pk2

[BeyondTheHorizon]

So I did a bit more messing around with GSC Unown, and I think the crash has something to do with PKHeX sometimes changing Unown's IVs and therefore its form upon trying to save, but not changing its sprite, resulting in confusion. If I produce the data above, go back to the Main tab to select its Form and double-check the Form its sprite shows (e.g. if its an X Unown, click on X to make absolute sure) IVs aren't changed and it seems to work. Sorry if I'm not explaining this very well.

Edited January 2, 2018 by BeyondTheHorizon
Added further information